What are the rules/laws for Congresspersons who want to listen to closed-door proceedings of committees they are not a part of?
[Depositions are covered the answer by Geobits.]
In the following, closed to the public means the same as closed-door.
My reading of the House rules is that, in reference to committees, closed to the public means that other House members may attend only when permitted, except for certain select committees.
With select committees1, other House members may attend unless exluded by a vote of the House when the select committee was established. The Permanent Select Committee on Intelligence was provided with rules allowing exclusion. The current select committees, with no apparent exclusion, are the Select Committee on the Climate Crisis and the Select Committee on the Modernization of Congress.
Text of the Rules and comments follow.
Committee on Ethics
Always closed under Rule XI 2(g)(1) (see below).
Committee on Appropriations
May be closed under Rule XI 2(g)(1) (see below) for national security.
Rule X 4(a)(1) A hearing under subdivision (A), or any part thereof, shall be held in open session, except when the committee, in open session and with a quorum present, determines by record vote that the testimony to be taken at that hearing on that day may be related to a matter of national security. The committee may by the same procedure close one subsequent day of hearing. A transcript of all such hearings shall be printed and a copy thereof furnished to each Member, Delegate, and the Resident Commissioner.
Permanent Select Committee on Intelligence
May be closed under Rule XI 2(g)(2) (see below) for national security.
Rule X 11(g)(3) The select committee shall, under such regulations as it may prescribe, make information described in subdivision (A) available to a committee or a Member, Delegate, or Resident Commissioner, and permit a Member, Delegate, or Resident Commissioner to attend a hearing of the select committee that is closed to the public. Whenever the select committee makes such information available, it shall keep a written record showing, in the case of particular information, which committee or which Member, Delegate, or Resident Commissioner received the information. A Member, Delegate, or Resident Commissioner who, and a committee that, receives information under this subdivision may not disclose the information except in a closed session of the House.
This clause means that the committee may permit others to attend. It does not require they do so.
For all other committees
Open meetings and hearings
Rule XI 2(g)
(1) Each meeting for the transaction of business, including the markup of legislation, by a standing committee or subcommittee thereof (other than the Committee on Ethics or its subcommittees) shall be open to the public, including to radio, television, and still photography coverage, except when the committee or subcommittee, in open session and with a majority present, determines by record vote that all or part of the remainder of the meeting on that day shall be in executive session because disclosure of matters to be considered would endanger national security, would compromise sensitive law enforcement information, would tend to defame, degrade, or incriminate any person, or otherwise would violate a law or rule of the House. Persons, other than members of the committee and such noncommittee Members, Delegates, Resident Commissioner, congressional staff, or departmental representatives as the committee may authorize, may not be present at a business or markup session that is held in executive session. This subparagraph does not apply to open committee hearings, which are governed by clause 4(a)(1) of rule X (see above) or by subparagraph (2).
(2) (A) Each hearing conducted by a committee or subcommittee (other than the Committee on Ethics or its subcommittees) shall be open to the public, including to radio, television, and still photography coverage, except when the committee or subcommittee, in open session and with a majority present, determines by record vote that all or part of the remainder of that hearing on that day shall be closed to the public because disclosure of testimony, evidence, or other matters to be considered would endanger national security, would compromise sensitive law enforcement information, or would violate a law or rule of the House.
(B) Notwithstanding the requirements of subdivision (A), in the presence of the number of members required under the rules of the committee for the purpose of taking testimony, a majority of those present may--
(i) agree to close the hearing for the sole purpose of discussing whether testimony or evidence to be received would endanger national security, would compromise sensitive law enforcement information, or would violate clause 2(k)(5) (see below); or
(ii) agree to close the hearing as provided in clause 2(k)(5) (see below).
(C) A Member, Delegate, or Resident Commissioner may not be excluded from non-participatory attendance at a hearing of a committee or subcommittee (other than the Committee on Ethics or its subcommittees) unless the House by majority vote authorizes a particular committee or subcommittee, for purposes of a particular series of hearings on a particular article of legislation or on a particular subject of investigation, to close its hearings to Members, Delegates, and the Resident Commissioner by the same procedures specified in this subparagraph for closing hearings to the public.
Note that (i), above, is for discussions about testimony and evidence and (ii) is for the actual testimony and evidence.
Note that, when subdivision (A) or (B) is invoked, subdivision (C) does not apply.
Subdivision (C) refers to select committees1, as suggested by the repeated use of particular. This subdivision was added in the 95th Congress.2
Rule XI 2(k)
(5) Whenever it is asserted by a member of the committee that the evidence or testimony at a hearing may tend to defame, degrade, or incriminate any person, or it is asserted by a witness that the evidence or testimony that the witness would give at a hearing may tend to defame, degrade, or incriminate the witness--
(A) notwithstanding paragraph Rule XI 2(2) (see above), such testimony or evidence shall be presented in executive session if, in the presence of the number of members required under the rules of the committee for the purpose of taking testimony, the committee determines by vote of a majority of those present that such evidence or testimony may tend to defame, degrade, or incriminate any person; and
(B) the committee shall proceed to receive such testimony in open session only if the committee, a majority being present, determines that such evidence or testimony will not tend to defame, degrade, or incriminate any person. In either case the committee shall afford such person an opportunity voluntarily to appear as a witness, and receive and dispose of requests from such person to subpoena additional witnesses.
Note that in (5) either a committee member or a witness may ask that the hearing be closed.
It is not clear, to me, how executive session in (A) differs from closed-door.
1Select committees are appointed to perform a special function that is beyond the authority or capacity of a standing committee, and expire on completion of their assigned duty.
2Jefferson's Manual, pp 216-217.
§ 410. Presence of a Member of the House in a select committee.
Any Member of the House may be present at any select committee, but cannot vote, and must give place to all of the committee, and sit below them. Elsynge, 12; Scob., 49.
In the 95th Congress, clause 2(g)(2) of rule XI was amended to prohibit the exclusion of noncommittee members from nonparticipatory attendance in any closed hearing, except in the Committee on Ethics, unless the House by majority vote authorizes a committee or subcommittee to close its hearings to noncommittee members (H. Res. 5, 95th Cong., Jan. 4, 1977, pp. 53–70). Formerly, a committee could close its doors in executive session meetings to persons not invited or required, including Members of the House who were not members of the committee (III, 1694; IV, 4558–4565; see discussion at IV, 4540).