ON DENIAL OF PETITION FOR REHEARING
HUNTLEY, Justice.The Idaho State Tax Commission (commission) appeals the district court’s order granting a writ of prohibition against the commission concerning the commission’s request to obtain certain documents to be used for appraisal purposes.
The commission appeals, claiming, among its assignments of error, that the district court applied an incorrect standard to determine the relevance of the information sought by the commission.
The Union Pacific Railroad and the Burlington Northern Railroad (railroads) own and operate national railway systems which operate in Idaho. The Idaho operating properties of both systems are assessed annually for ad valorem tax purposes by the commission. The commission values the railroads based on their market values. IDAPA 35.03. 202.a. To aid the commission in preparing these assessments, the railroads are required by I.C. § 63-701 et seq. to provide certain information to the commission.
As part of the assessment process the commission wrote to the railroads in January 1984 enclosing the blank annual statement forms required under I.C. § 63-706 and amending the notice section of the form to request several documents including “a copy of any long-range or strategic plan prepared in whole or in part during the calendar year 1983.” The railroads filed a motion to quash the request with the commission. The motion was denied.
The railroads petitioned the district court for a writ of prohibition to quash the requests of the commission. At trial, the railroads produced three witnesses to show that the strategic plans were “forward looking” and too speculative to be effectively used in the assessment process. Mr. Rebensdorf, the vice president for planning *1002analysis for Union Pacific Railroad, testified: (1) that the distribution of the strategic plan was generally limited to high-level management personnel in the Union Pacific Railroad; (2) that the strategic plan is a “living document” which changes over time; (3) that the release of information in the strategic plan to a competitor would be harmful and therefore its production would have a chilling effect on the railroads’ planning process; and (4) that the release of the information to the commission would lead to general release because the commission would release the information to the Multi-State Tax Commission. Mr. Strong, employed by the commission for about seven years as an appraiser of railroad and utility properties, testified that he had never heard of a strategic plan being used in an appraisal and that he did not believe that such a plan would be useful in the appraisal process. He testified that he had appraised over 180 companies. Dr. Pratt, a financial analyst, testified that a strategic plan has no part in the valuation process because it depends on the occurrence of events which are not certain to happen and is biased by the analyst’s hopes and expectations about the future of the company. He testified that an appraisal should be based on what the company is worth now and not what someone in the company believes it will be worth in the future. He testified that reliable information concerning the railroads can be had from investment banks at a low cost.
The commission produced two witnesses to show that the strategic plan could be used in some assessment procedures. Mr. Goodwin, an appraiser from Kansas, testified that some assessors use what is known as the discounted cash flow model of appraisal. He testified that “for appraising under this model, some elements [of the strategic plan] would be very helpful.” He also testified that other sources of information about the future value of the railroads is more expensive than the railroads’ testimony would indicate. Mr. Goodwin testified that he believed that the strategic plan would provide more accurate information than could be found in the marketplace because management has a better view of the company’s performance than most analysts. Dr. Cornell, a U.C.L.A. professor, testified for the state that the strategic plan would be useful in assessing a utility under the discounted cash flow method. Finally, counsel for the commission argued that the strategic plan contains many conclusions and projections which are relevant to the assessment process. Primarily, the plan may contain a resolution of whether the cash flow from railroad assets is expected to grow due to inflationary pressures which were predictable at the time of the assessment. Counsel argued that such potentially relevant material as cap rate determinations, equipment expense projections, replacement costs, and inflation rate predictions for labor costs, capital costs and revenue increases might appear in the strategic plan. According to counsel, the plan might also contain predictions concerning regulatory changes and other forces affecting the competitive environment of the railroads, all of which could affect the market value of the railroad.
The district court held that the following standard applies to determine the relevance of information requested by the commission:
1. The demand for the strategic plans must not exceed the commission’s investigatory powers.
2. The strategic plans must be reasonably relevant to the commission’s purpose.
3. The commission’s need for the plans must outweigh the burden suffered by the railroads in releasing the information.
The district court accepted Cooper’s interpretation of this rule:
[i]f the agency has made an initial showing that the desired information may be reasonably relevant, the burden shifts to the respondent to disprove its relevancy; and the courts are generally inclined to overrule a defense of irrelevancy unless the party resisting the subpoena makes it appear plainly to the court that the documents in question are clearly irrelevant, *1003or that they have no potential relevancy.
1 F. Cooper, State Administrative Law, 301 (1965).
The court held that the commission did not meet its burden of proving the relevance of the information because the court heard no evidence to indicate that Idaho would use the discounted cash flow method of appraisal, the only method to which the strategic plan might be relevant. Further, the court held that the damage to the railroads from releasing the information would be greater than the commission’s need for the information.
I.
The district court chose the correct standard to determine the relevance of the information requested by the commission. It has long been established that the court should grant significant deference to the discovery requests of administrative agencies. See United States v. Morton Salt Co., 338 U.S. 632, 70 S.Ct. 357, 94 L.Ed. 401 (1950). As stated in Morton Salt: “[I]t is sufficient if the inquiry is within the authority of the agency, the demand is not too indefinite and the information sought is reasonably relevant. ‘The gist of the protection is in the requirement, expressed in terms, that the disclosure sought shall not be unreasonable.’ ” 338 U.S. at 652-653, 70 S.Ct. at 369, quoting Oklahoma Press Publishing Co. v. Walling, 327 U.S. 186, 208, 66 S.Ct. 494, 505, 90 L.Ed. 614 (1946). Both federal and state courts have interpreted Morton Salt to require a test substantially similar to that used by the district court. See, e.g., Dow Chemical Co. v. Allen, 672 F.2d 1262, 1266 (7th Cir.1982); Central Maine Power Co. v. Maine Public Utilities Commission, 395 A.2d 414, 426 (Me.1978); Yellow Freight Systems, Inc. v. Kansas Commission on Civil Rights, 214 Kan. 120, 519 P.2d 1092, 1096 (1974).
II.
The district court correctly ruled that the initial burden of proving the relevance of the requested documents is on the commission. Placing the burden of proof on the commission is in accord with United States Supreme Court authority. United States v. Powell, 379 U.S. 48, 57-58, 85 S.Ct. 248, 255, 13 L.Ed.2d 112 (1964). In Powell, the Court said about the Commissioner of Internal Revenue’s attempts to discover certain materials that the Commissioner “must show that the investigation will be conducted pursuant to a legitimate purpose, that the inquiry may be relevant to the purpose, that the information sought is not already within the Commissioner’s possession, and that the administrative steps required by the Code have been followed____” [Emphasis added.] Under Powell, the Idaho State Tax Commission had the initial burden of proving the relevance of the railroad’s strategic plan to the valuation of the railroad.
On Petition for Rehearing Union Pacific urges that no evidence demonstrated the necessity of the strategic plan to proof of the railroad’s value and that the district court therefore properly refused discovery of the plan. The argument does not persuade us for three reasons. First, the test is one of relevancy, not necessity. Second, even though it might be possible to formulate a valuation without the data contained in the plan, that data is relevant if it would assist in arriving at a more accurate or appropriate appraisal or appraisal technique. Third, even Union Pacific admits the plan could be relevant to contradict or impeach other evidence of valuation. In that capacity the plan would be relevant to valuation.
During oral argument before this court, counsel for the tax commission stated he had demanded in camera review of the strategic plan by the trial court as a preface to ruling on its production and admission. Counsel for Union Pacific did not dispute this assertion at oral argument. Union Pacific now contends that the transcript on appeal reflects no such demand and that the issue was therefore lost for purposes of appeal.
*1004The pre-trial district court proceedings included a petition for writ of prohibition blocking the tax commission from discovery of Union Pacific’s strategic plan. The trial hearings took place on July 9 and 10, 1984. On December 14, 1984, the district court filed a memorandum decision granting the writs. Whether the commission made such a demand is determinative of whether the failure to conduct an in camera review is appealable.
If on further hearing before the trial court it is determined that the commission did request an in camera review, this court’s opinion stands as hereinabove written. If, on the other hand, further hearing results in a determination by the trial court that the commission made no demand upon the district court for an in camera review, then that issue was lost for purposes of appeal and the district court’s denial of the commission discovery request for the strategic plan is affirmed. See In re Bowen, 95 Idaho 334, 508 P.2d 1240 (1973); Hamley v. J.R. Simplot Co., 94 Idaho 794, 498 P.2d 1267 (1972); Beehive Medical Electronics, Inc. v. Square D. Co., 669 P.2d 859 (Utah 1983).
Costs to appellants.
DONALDSON, C.J., and BISTLINE, J., concur.