I dissent. The majority render section 32 of article XIII of the California Constitution (hereafter section 32) a nullity by requiring that the board must establish that the strategic plan must in fact be relevant to the board’s consideration of Union Pacific’s tax return rather than that it might be relevant. This is a critical distinction because the entire thrust of section 32 is to ensure that the collection of taxes continues unabated while a taxpayer and the government litigate a dispute about the assessment and collection of taxes. (Pacific Gas & Electric Co. v. State Bd. of Equalization (1980) 27 Cal.3d 277, 283 [165 Cal.Rptr. 122, 611 P.2d 463]; Modern Barber Col. v. Cal. Emp. Stab. Com. (1948) 31 Cal.2d 720, 726 [192 P.2d 916].)
If the board is required to prove the actual relevance of the information it seeks before Union Pacific is required to pay the tax or the penalty, section 32 serves no purpose. (Cf. Enochs v. Williams Packing Co. (1961) 370 U.S. 1, 8 [8 L.Ed.2d 292, 297, 82 S.Ct. 1125].) As discussed below, we are required to give effect to section 32 to the maximum extent consistent with the Fourth Amendment of the United States Constitution, and that provision does not require this court to test the board’s entitlement to the information it seeks by the stringent standard applied by the majority. A correct analysis of the relevance issue leads to the conclusion that the trial court did not have jurisdiction to prohibit the board from obtaining the information sought by the board’s subpoena.
Moreover, in the course of their opinion the majority virtually abrogate the board’s right to obtain information from a taxpayer (Rev. & Tax. Code, § 826 et seq.) by holding that the taxpayer is not required to disclose any of the information sought if some of it is not relevant.
*160I outline initially what I view as the appropriate principles which the majority should have applied to the board’s request for information from Union Pacific. As noted above, the purpose of the provision of section 32 depriving a court of jurisdiction to suspend the collection of taxes is to ensure that collection continues unabated while a taxpayer and the government litigate a dispute regarding their imposition. The validity of the tax is thereafter determined in a suit by the taxpayer for refund. Because any delay in collection may cause serious detriment to the public, courts have been “extremely reluctant” to interfere in the taxation process before the taxpayer pays the levies assessed. (Pacific Gas & Electric Co. v. State Bd. of Equalization, supra, 27 Cal.3d 277, 282.) We held in Western Oil & Gas Assn. v. State Bd. of Equalization (1987) 44 Cal. 3d 208 [242 Cal.Rptr. 334, 745 P.2d 1360] (hereafter Western Oil) that since a request for information by the board is a first step in the assessment and collection of taxes, section 32 broadly limits the power of a court to prevent the taxing authority from obtaining the information it seeks prior to the time the tax is collected. The ultimate validity of the assessment is not the issue; a court may only examine the board’s authority to undertake the inquiry. (44 Cal. 3d 208, 214.) Exceptions to the command of section 32 must be narrowly construed in order to carry out the purpose of the section.
We further made clear in Western Oil that section 32 must be given effect to its maximum extent, limited only by the provisions of the United States Constitution, and that the appropriate standard for judicial intervention is the one invoked under a federal statute which contains provisions similar to section 32. (44 Cal.3d at pp. 212-213.)1
The federal statute is interpreted liberally in favor of the government. (Enochs v. Williams Packing Co., supra, 370 U.S. 1, 7-8 [8 L.Ed.2d 292, 296-297].) The power of the government to obtain information from a taxpayer has frequently been compared to the powers of investigation of a grand jury; issues of materiality and relevancy are essentially the same as those applied to grand jury investigations. (See, e.g., United States v. Ryan (9th Cir. 1971) 455 F.2d 728, 733 [20 A.L.R.Fed. 719]; Foster v. United States (2d Cir. 1959) 265 F.2d 183, 186-187.) Because the burden on the government would be too great if it were required to prove the relevance of material which it does not have by the standards applied to the admissibility of evidence at trial, it need not prove that the information is actually relevant in any technical, evidentiary sense. (La Mura v. United States (11th Cir. 1985) 765 F.2d 974, 981.)
*161In applying the “reasonable relevance” test called for by the Fourth Amendment the federal cases uniformly hold that to justify a request for information, the government is required to show only that the material sought has potential relevance to an investigation. It meets this burden by showing that the information “might throw light upon the correctness of the taxpayer’s return” or “illuminate any aspect of the return.” (See, e.g., United States v. Arthur Young & Co. (1984) 465 U.S. 805, 813-815 [79 L.Ed.2d 826, 833-835, 104 S.Ct. 1495]; Matter of Newton (11th Cir. 1983) 718 F.2d 1015, 1019; United States v. Southwestern Bank & Trust Co. (10th Cir. 1982) 693 F.2d 994, 996; United States v. City Nat. Bank & Trust Co. (10th Cir. 1981) 642 F.2d 388, 389; United States v. Goldman (9th Cir. 1980) 637 F.2d 664, 667; United States v. Wyatt (5th Cir. 1981) 637 F.2d 293, 300; United States v. Freedom Church (1st Cir. 1979) 613 F.2d 316, 321; United States v. Davey (2d Cir. 1976) 543 F.2d 996, 1000; United States v. Ryan, supra, 455 F.2d 728, 733; United States v. Leaseway Transp. Corp. (N.D.Ohio 1981) 523 F.Supp. 1333, 1338; United States v. Campbell (D.S.D. 1975) 390 F.Supp. 711, 713.)2 The government must have a “realistic expectation rather than an idle hope that something might be discovered.” (United States v. Wyatt, supra, 637 F.2d 293, 300-301.) This is the standard which the majority should apply, but fail to do so without explanation or even recognition of the existence of the rule.
Instead of exercising “extreme reluctance” to interfere in this prepayment challenge, the majority resolve every doubtful point against the board’s position, make unwarranted and unsupported assumptions to justify Union Pacific’s resistance to the subpoena, and even resolve conflicting claims as to the proper valuation method applicable to the assessment of Union Pacific’s property against the board’s position.
The fundamental premise on which the majority hold that the strategic plan is not relevant is that the market value of Union Pacific’s property cannot be affected by the railroad’s plans to acquire property in the future (maj. opn., ante, at p. 148) and that an acquisition can only affect existing value when it takes place (maj. opn., ante, at p. 152). These conclusions are not based on any evidence in the record but simply on the unsupported assumptions of the majority. The fact present value can be affected by a planned acquisition is demonstrated by the analogous situation of the stock market. Every day; stocks rise and fall in the stock market on the basis of *162reports that one corporation may acquire the assets of another. Obviously, the likelihood that information relating to the acquisition of future assets will affect the current value of a corporation depends on the probability that the acquisition will occur, the imminence of the acquisition, the value which the property to be acquired will add to the purchaser, and other such factors. Of course, a buyer of shares might not know definitely that the acquisition will occur, but even a rumor of the acquisition may induce him to pay a higher price for the corporation’s stock. On the other hand, the potential buyer of a railroad would doubtless be informed of the planned acquisition if the purchase would enhance the value of the railroad and thus the purchase price. In any event, it seems to me unarguable that future acquisitions might affect the present value of Union Pacific’s property.3 This is all that is required by the Fourth Amendment to justify the board’s request for disclosure of Union Pacific’s plan.
Contrary to the majority opinion, the decision of the Idaho Supreme Court in Union Pacific R. Co. v. Looney (1986) 111 Idaho 1000 [729 P.2d 1063] provides persuasive authority that the strategic plan might throw light on the evaluation of Union Pacific’s tax return. The majority fail to point out that Union Pacific conceded before the Idaho court that information as to its corporate plan—substantially the same information the board seeks here—“could be relevant to contradict or impeach other evidence of valuation.” (729 P.2d at p. 1066.)4 Furthermore, the majority state that the *163Idaho Supreme Court noted only that the plan “could be relevant” but “never squarely held that it was.” (Maj. opn., ante, at p. 151.) Under a correct application of the relevancy standard, a determination that the plan “could be relevant” is sufficient to justify the demand for disclosure. In any event, the court concluded that if the plan could be relevant it “would be relevant to valuation” {ibid.), and therefore disclosure would be required.5
Another example of the majority’s failure to consider the board’s assertion of relevancy by the appropriate standard is its rejection of the board’s “multiplier approach.” They hold that the board was not entitled to discovery of the strategic plan because it claimed that the plan was necessary in order for it to apply the “multiplier” method of computation. That method was not appropriate here, hold the majority, because its use depends on evidence of comparative sales, and a member of the board’s staff testified that there were no properties available for comparison. (Maj. opn., ante, at pp. 154-155.) This statement was made during hearings held by the board to determine the appropriate method of valuation, and there was sharp disagreement in the testimony of witnesses for Union Pacific and the board’s staff on that issue. Indeed, it was Union Pacific’s own expert who claimed that the board should have and did not use the “multiplier” method. It is inappropriate to decide at this stage that the board was not entitled to adopt a particular method of valuation and that, therefore, it must be denied the information which it seeks in order to apply the valuation method it deems appropriate. This is but another example of the majority’s failure to be bound by the constraints imposed on this court in considering the validity of a prepayment challenge by a taxpayer to a request for information.
*164The majority’s determination that the board was not entitled to discover relevant portions of the strategic plan because some parts of the plan might be irrelevant is also, in my view, clearly erroneous. (Maj. opn., ante, at pp. 152-153.)6 If some parts of the plan are irrelevant, the solution is not to deny discovery of the entire plan but to require the court to examine the plan in camera so that it may separate the relevant from the irrelevant parts of the plan. (Valley Bank of Nevada v. Superior Court (1975) 15 Cal. 3d 652, 658 [125 Cal.Rptr. 553, 542 P.2d 977] [“The trial court has available certain procedural devices which may be useful in fashioning an appropriate order that will, so far as possible, accommodate considerations of both disclosure and confidentiality. These include . . . the holding of in camera hearings. There may well be others which ingenious courts and counsel may develop.”].) This is a procedural device often employed by trial courts to protect the confidentiality of information when discoverable and nondiscoverable materials are contained in the same document. (E.g., In re Lifschutz (1970) 2 Cal.3d 415, fn. 23 at p. 437 [85 Cal.Rptr. 829, 467 P.2d 557, 44 A.L.R.3d 1] [“[T]he trial judge should take necessary precautions to protect . . . confidentiality ... for example, he might routinely permit . . . disclosure to be made ex parte in his chambers.”]; El Dorado Savings & Loan Assn. v. Superior Court (1987) 190 Cal.App.3d 342, 346 [235 Cal.Rptr. 303] [“[Respondent court should first examine the file in camera and order disclosure of only that information which might be relevant to the lawsuit”]; Saddleback Community Hospital v. Superior Court (1984) 158 Cal.App.3d 206, 209 [204 Cal.Rptr. 598] [“To protect both parties . . . there must be an in camera hearing by the trial court . . . . [¶] . . . ‘[W]here an exception to a privilege depends on the content of a communication, the court may require disclosure in camera in making its ruling.’ ”]; Fellows v. Superior Court (1980) 108 Cal.App.3d 55, 68 [166 Cal.Rptr. 274] [“In order for the trial judge to rule on the claim of. . . privilege . . . it is necessary for the court to make an in camera inspection of these documents.”]; Mavroudis v. Superior Court (1980) 102 Cal.App.3d 594, 605 [162 Cal.Rptr. 724] [“The court should initially examine the records in camera to determine if the material therein reveals that petitioners were readily identifiable as victims . . . .”]; County of Kern v. Superior Court (1978) 82 Cal.App.3d 396, 401-402 [147 Cal.Rptr. 248] [“The ... file .. . should be *165carefully examined by the trial court in an in camera hearing to excise . . . any part derived from the work of a protected committee.”].)
The majority’s denial of an in camera inspection on the ground that the board did not make such a request is erroneous. In none of the cases cited above did the litigant make such a request. Whatever may be the rule in Idaho, the cases cited above make it clear that no request for an in camera inspection is required in California, and that such an inspection is made on the trial court’s own motion in order to enable it to rule properly on a request for discovery. In all these cases, the failure by the trial court to hold an inspection to avoid disclosure of confidential information was held erroneous or the court was simply ordered to make the inspection. Neither these cases nor any others cited or found in this state imply that a request for an in camera hearing is necessary.7 Clearly, the trial court may be required to conduct an in camera examination on its own motion when it is necessary to grant discovery of part but not all of a document.
I just cannot see how this court can deny the right of the board, a government agency acting in the public interest, to have an in camera determination by the trial court of the relevance or existence of material sought for taxing purposes. If the trial court finds that some of the material is irrelevant, discovery as to that material is denied and the taxpayer is protected. But if some of it is relevant, then discovery should be ordered.
If, as I conclude, the trial court had no jurisdiction to enjoin the board from enforcing the subpoena, it follows that it also lacked jurisdiction to prohibit the board from enforcing the penalty assessment.
The consequence of the majority’s holding is to encourage taxpayers to resist board subpoenas. By claiming that some of the material sought is irrelevant the taxpayer may bar the government from further inquiry. If he asserts that the subpoena is invalid because all the documents demanded are irrelevant, he imposes on the board the burden of proving by the standards *166applicable to a full-blown trial that the information is in fact relevant to the board’s inquiry, even if that may require the board to prove such detailed matters as the justification for its method of valuation. It may and often will take years for a final determination of these complex matters. (In the present case, for example, it has been five years since Union Pacific filed its petition for a writ of mandate.) If the government ultimately prevails, during the period of litigation the taxpayer will have avoided payment of both the taxes which might result if the information had been provided and the penalty which was imposed for failure to provide the information. Since the purpose of section 32 is precisely to place the disputed sums in the hands of the government while the parties litigate the validity of the tax, the majority abrogate that provision by their holding.
Broussard, J., concurred.
Appellant’s petition for a rehearing was denied September 28, 1989. Broussard, J., was of the opinion that the petition should be granted.
The federal statute provides in pertinent part, “[N]o suit for the purpose of restraining the assessment or collection of any tax shall be maintained in any court by any person . . . .” (26 U.S.C. § 7421(a).)
The seminal case on the question of the Internal Revenue Service’s (IRS) right to obtain information from a taxpayer under the Fourth Amendment is United States v. Powell (1964) 379 U.S. 48, 57-58 [13 L.Ed.2d 112, 119-120, 85 S.Ct. 248]. It holds that the IRS needs to show only that the information it seeks may be relevant to a legitimate purpose. The federal courts have consistently construed this language as imposing the “might throw light” test.
Union Pacific’s value for tax purposes is measured by the value of all its property viewed as a unit. (Maj. opn., ante, at pp. 148-149, fn. 9.) This is the same measurement used to determine the value of a corporation’s stock. But even if the analogy is not wholly sound, how can it be said that Union Pacific’s present value cannot be affected by a planned acquisition?
A simple hypothetical: Suppose Union Pacific’s tracks for passenger trains go within one mile of Disneyland, and the company has plans to acquire within the next few months—either by purchase or condemnation—a right of way for the intervening mile so as to carry passengers to Disneyland. Might not a buyer, informed of this plan, assess the likelihood that the purchase will be made or the property will be taken by eminent domain, and be willing to pay a higher price for the company’s assets on the basis that its value is greater than indicated by the property it presently owns? I do not see how the majority can say that the company’s plan to acquire the facility could not affect its value (maj. opn., ante, at p. 149, fn. 11), particularly if the acquisition was reasonably certain and imminent.
This concession is plain on the face of the Looney opinion. The majority’s surmise that the concession might have applied only to parts of the plan (maj. opn., ante, at p. 151, fn. 12) is wholly an invention of the majority. There is not the slightest hint on the face of the Looney opinion to support this contorted analysis of Union Pacific’s concession that the plan “would be relevant.”
I note also that the majority disapprove of assertedly inconsistent positions taken by the board regarding the relevance of future acquisitions. (Maj. opn., ante, at p. 150.) This disapproval apparently extends only to the government and not to a taxpayer. Not only did Union Pacific concede in Looney that the information regarding its future acquisitions could be relevant to the government, but, as we shall see, in the present litigation it insisted that the board *163adopt the “multiplier” method of computation. Yet Union Pacific claims before this court that this method is inappropriate, and the majority agree.
I also disagree with the majority’s determination that the Looney decision does not amount to a holding on the issue of relevance of the plan. (Maj. opn., ante, at p. 151.) It is true that the Idaho Supreme Court remanded the matter to the trial court for a determination whether the taxing commission had made a request for an in camera inspection of the plan and held that if no such inspection had been requested then the commission was not entitled to discover the plan. But this ruling appears to refer to an additional factual issue in the Looney case, i.e., the correctness of the lower court’s finding that the damage to Union Pacific from releasing the information would be greater than the tax commission’s need for it. The evaluation of this claim obviously requires an in camera inspection of the material sought. On the issue of relevance, the court clearly held that Union Pacific admitted that the plan could be relevant, and that in view of that concession the plan “would be relevant.”
Nor do I agree with the majority’s statement that Looney is distinguishable because the Idaho court was “primarily concerned with information as to existing assets rather than possible future acquisitions.” (Maj. opn., ante, at p. 151.) The discovery motion considered in Looney was directed entirely to any “long-range or strategic plan prepared . . . during the calendar year 1983,” and all the evidence discussed in the opinion related to the relevance of future acquisitions to the present value of a railroad.
This holding appears on pages 152-153 of the majority opinion . The opinion states that “even if information as to Union Pacific’s future purchases of replacement track and rolling stock is relevant. . . the relevance of that limited information does not mean that all other information as to future acquisitions ... is also relevant.” (Italics added.) The opinion then goes on to deny an in camera inspection. This amounts to a determination that the board was not entitled to discover Union Pacific’s plan for future purchases of replacement track and rolling stock, even though relevant, because other types of future acquisitions may be irrelevant.
The majority’s attempt to distinguish these cases on the ground that the party seeking discovery had no incentive to request an in camera hearing because he prevailed in the trial court is erroneous. (Maj. opn., ante, at pp. 153-154, fn. 14.) In Mavroudis, supra, 102 Cal.App.3d 594, the trial court denied discovery, yet the appellate court ordered it to conduct an in camera hearing to separate discoverable from nondiscoverable information, although there is no indication that the losing party had made a request for such a hearing. Nor is it significant that some of the cases cited above involved a privilege granted by statute. Whether the privilege is granted by statute or involves a constitutional right to privacy (as in El Dorado Savings & Loan Assn. v. Superior Court, supra, 190 Cal.App.3d 342, 346), or merely an overly broad request for discovery, the rule is the same: the trial court must hold an in camera hearing on its own motion if such a hearing is necessary to decide whether a request for discovery should be granted.