announced the judgment of the Court, and delivered an opinion in which JUSTICE COMPTON and JUSTICE RUSSELL join.
In this case we consider whether an itemized list of long distance telephone calls placed by the Governor’s office must be disclosed when requested pursuant to the Freedom of Information Act, Va. Code §§ 2.1-340, et seq.
The special projects editor of The Daily Progress, a newspaper published by Worrell Enterprises, Inc. (Worrell), requested copies of the monthly billings sent by the Department of Information Technology to the Governor’s office for telephone service to that office. The request, submitted under the Freedom of Information Act (the Act), sought each page detailing information about “SCATS and toll calls, long-distance and third party calls” since January 13, 1990.
The information contained on the itemized billings includes a cover sheet which lists the aggregate monthly charges for various phone services.1 The remaining pages identify individual toll calls by the telephone number charged for the call, the city and number called, and the city and number from which the call was placed. The itemization also shows the number of minutes of each conversation and the charge for each.2
Richard D. Taylor, Jr., Special Assistant to the Governor and custodian of the telephone records for the Governor’s office, agreed to provide Worrell with the cover sheet showing the aggregate charges. Taylor denied Worrell’s request for the itemized billings for each toll call, maintaining that these records were exempt from disclosure under § 2.1-342(B)(4) of the Act as “[mjemoranda, working papers and correspondence held ... by the office of the Governor.”
Worrell filed a petition for writ of mandamus. The trial court, after considering argument of counsel, determined that the information did not come within the terms of the pertinent exception *221and, therefore, was subject to compelled disclosure under the Act. Subsequently, the court entered an order granting the writ on November 15, 1990. We awarded Taylor an appeal.
The Attorney General argues, inter alia, that the Act, as interpreted by the trial court to require mandatory disclosure of these telephone records, violates the separation of powers doctrine embodied in article I, § 5 and article III, § 1 of the Virginia Constitution.
In considering this issue, we are mindful of the presumption of validity that attaches to a statute, that requires this Court to resolve any reasonable doubt as to the statute’s constitutionality in favor of its legality if possible. Infants v. Virginia Hous. Dev. Auth., 221 Va. 659, 669, 272 S.E.2d 649, 655 (1980); Allen v. The Governor, 151 Va. 21, 24, 144 S.E. 469, 475 (1928); Carter’s Case, 96 Va. 791, 815, 32 S.E. 780, 785 (1899).
The Virginia Constitution directs that the government function through three equal but separate branches with specific responsibilities and powers assigned to each, and that no one branch may exercise the functions or powers of another except as specifically authorized by the constitution. Gandy v. Elizabeth City County, 179 Va. 340, 346, 19 S.E.2d 97, 99 (1942); Commonwealth v. Dodson, 176 Va. 281, 305, 11 S.E.2d 120, 131 (1940). Va. Const. art. I, § 5, art. III, § 1. This principle prevents one branch from engaging in the functions of another, such as the judicial branch performing a legislative function Bd. of Supervisors of Fairfax Co. v. Allman, 215 Va. 434, 211 S.E.2d 48 (1975), Gandy, supra, or the legislative branch taking on powers of a judicial nature, Fugate v. Weston, 156 Va. 107, 157 S.E. 736 (1931).
In considering separation of powers issues, however, we have acknowledged that the degree of separation demanded by the Virginia Constitution is not absolute and necessarily operates within some practical limitations and exceptions. Baliles v. Mazur, 224 Va. 462, 472, 297 S.E.2d 695, 700 (1982). The legislative branch may delegate some of its powers to agencies in the executive branch if the delegation is accompanied by appropriate standards for the exercise of that authority. Ames v. Town of Painter, 239 Va. 343, 349, 389 S.E.2d 702, 705 (1990). There will also be instances where the line between the powers of two branches may be *222less than clear and incidental encroachment is necessary and permitted.3 Fugate, 156 Va. at 112, 157 S.E. at 737.
Nevertheless, the legislature may run afoul of the separation of powers doctrine even though it is exercising legitimate regulatory authority. In Carter’s Case, supra, the legislature’s authority to regulate the use of the power of contempt of court was balanced with the judiciary’s inherent right to exercise that power. This Court held that legislative regulation of the contempt power was legitimate; however, it could not interfere with the courts’ contempt power to the extent that the power was rendered ineffectual, or to the extent that it destroyed the “authority necessary to the exercise of the jurisdiction conferred” on the courts. Id. at 816, 32 S.E. at 785; see Yoder v. Commonwealth, 107 Va. 823, 829-30, 57 S.E. 581, 583-84 (1907).
Worrell argues that legislatively required disclosure of the itemized statements does not encroach on the Governor’s constitutional responsibilities as Chief Executive Officer because the content of the telephone calls remains confidential. Therefore, the argument goes, the legisláture did not compromise the executive’s consultation and decision-making process and there is no violation of the separation of powers doctrine.
Worrell’s argument incorrectly presumes that the data sought are totally devoid of substantive information. On the contrary, data which show the time and the originating and terminating location of a call is information concerning the activity of the Governor’s office. The data, standing alone, could provide a basis for public speculation. The data also provide an information base for further investigation which could subject recipients of such calls to inquiries regarding the calls and their content.
More importantly, as argued by the Attorney General, compelled release of this information could have a chilling effect on the Governor’s use of the telephone for conducting the Commonwealth’s business. The Governor’s need to confer with persons located in a different city, as well as the need to confer with his office while out of Richmond, cannot seriously be disputed. The *223potential chilling effect would operate not only on the Chief Executive but could also extend to individuals he might wish to consult via this communication medium. As noted by the United States Supreme Court,
[h]uman experience teaches that those who expect public dissemination of their remarks may well temper candor with a concern for appearances and for their own interests to the detriment of the decision making process.
United States v. Nixon, 418 U.S. 683, 705 (1974). A lack of candor or an unwillingness to participate in the decision making process is as likely to flow from the compelled disclosure of the fact of consultation as from the disclosure of the content of the consultation. See Levi, Some Aspects of Separation of Powers, 76 Colum. L. Rev. 371, 388-390 (1976).
Thus, contrary to Worrell’s premise, the data requested have an intrinsic significance apart from the content of the calls themselves. Compelled disclosure of that data impairs, though it does not completely destroy, the ability of the executive to perform his constitutionally required duties. The appropriate considerations for determining whether the interference is sufficient to constitute a violation of the separation of powers doctrine were succinctly articulated by the United States Supreme Court in Nixon v. Administrator of Gen. Servs., 433 U.S. 425, 443 (1977) (citations omitted):
[I]n determining whether the Act disrupts the proper balance between the coordinate branches, the proper inquiry focuses on the extent to which it prevents the Executive Branch from accomplishing its constitutionally assigned functions .... Only where the potential for disruption is present must we then determine whether that impact is justified by an overriding need to promote objectives within the constitutional authority of Congress.
We have already said that compelled disclosure of the information at issue presents a “potential for disruption.” We now turn to whether this potential disruption is justified by “an overriding need to promote objectives” of the legislative branch. The legislative objective here is not one of providing a means for conducting an investigation or prosecution of the executive branch for alleged *224misconduct. Rather, the legislative objective is to encourage and facilitate a policy of openness in government. We must determine, then, if this policy justifies the disruption attendant to the compelled disclosure of the information at issue.
The General Assembly’s implementation of an open government policy is realized by the Act itself. The General Assembly sought to ensure public access to governmental records and meetings, to avoid an “atmosphere of secrecy” in the conduct of government affairs, and to encourage resolution of disputes in these areas through agreement rather than litigation. § 2.1-340.1. The General Assembly does not consider the policy absolute, however, and currently has identified 44 instances in which certain information is exempt from mandatory disclosure. Taken together, these exemptions reflect the General Assembly’s determination that the policy of openness does not override the need for confidentiality in every circumstance, that the best interests of the Commonwealth may require that certain governmental records and activities not be subject to compelled disclosure. Furthermore, the parties agree that the exemption in issue reflected the General Assembly’s recognition of “constitutional limits on its ability to invade the confidentiality of the Governor’s communications.”
Thus, we cannot say that the potential for disruption imposed on the Governor in executing the duties of Chief Executive Officer is outweighed by the application of the open government policy in this instance. Consequently, a legislatively imposed disclosure requirement would constitute a violation of the separation of powers doctrine because disclosure of the information in question would unduly interfere with the Chief Executive Officer’s ability to perform his duties, and is not warranted by an overriding need to promote a policy of open government in this instance.
Viewing the Act as a whole, and presuming that the General Assembly acted within constitutional parameters, we conclude that the General Assembly intended to exclude from mandatory disclosure information which, if required to be released, would unconstitutionally interfere with the ability of the Governor to execute the duties of his office. Therefore, the information at issue here must fall within the § 2.1-342(B)(4) exemption and is not subject to compelled disclosure under the Act.
*225Accordingly, we will reverse the judgment of the trial court and dismiss the petition for writ of mandamus.
Reversed and dismissed.
Although the itemized billings in issue are not part of the record, the parties have stipulated that they are in the same form as the itemized billing examples attached to Worrell’s petition. The cover page shows the charges for main line, long distance, SCATS, cellular phone, data, video conferencing, message units, radio, and pager services. The current version of this page combines certain of these services, but retains separate identification of costs incurred for SCATS calls and toll calls.
Calls placed on the SCATS network do not reflect the city or number called but show only the total number of minutes each originating telephone number utilized the SCATS system and the accompanying charge.
Similarly, the distinction between executive privilege and separation of powers is not always clear. Executive privilege reflects the need of the executive to withhold information requested pursuant to a legitimate exercise of governmental authority. See Nixon v. Administrator of Gen. Servs., 433 U.S. 425, 447 (1977). A violation of the separation of powers doctrine — the improper invasion by one branch of government into the province of another — is not a prerequisite for the assertion of the executive privilege doctrine.