Is this what they are referring to?
House Committee Hearings: The “Minority Witness Rule”August 14, 2015 (RS22637)
When a House committee or subcommittee holds a hearing, the minority party members of the panel have the right to call witnesses of their choosing to testify on at least one day of that hearing. Clause 2(j)(1) of House Rule XI—known as the “minority witness rule”—states:
Whenever a hearing is conducted by a committee on a measure or matter, the minority members of the committee shall be entitled, upon request to the chairman by a majority of them before the completion of the hearing, to call witnesses selected by the minority to testify with respect to that measure or matter during at least one day of hearing thereon.
If the minority’s request to call witnesses comes after a hearing has begun, it will necessitate the continuation of the hearing on an additional day to accommodate minority witnesses.1 Rule XI, however, is rarely formally invoked to request an additional day of hearing. In practice, the rule has largely served as a “backstop” that gives the minority party a procedural recourse if a committee majority refuses to invite witnesses they request. In the vast majority of hearings, the majority does invite minority witnesses after consultation and negotiation with minority members and staff. In rare instances, however, a majority of the minority party members of a House committee or subcommittee have invoked Rule XI to schedule an additional day of hearings for their witnesses.