The House Ethics Committee acknowledged Monday it is investigating Reps. Ben Ray Luján, John Conyers and House staffer Michael Collins.

The panel did not disclose details of its inquiry. Since the probe was referred to the House committee by the Office of Congressional Ethics, details of the OCE’s reports are expected to be made public August 9.

It is unclear if the inquiries are related, but all three cases were sent to the committee by OCE on May 11. The announcement kicks off a 45-day public comment period required by the panel after a referral is transmitted to the committee from OCE. The OCE is independent of Congress.

Luján is the chairman of the Democratic Congressional Campaign Committee from New Mexico. Conyers, a Democrat from Michigan, is considered to be the dean of the House as the chamber’s longest continuously serving member.

Collins has served for many years as chief of staff for Rep. John Lewis, D-Ga.

Joe Shoemaker, a spokesman and senior advisor to Lujan, said in a statement the inquiry  relates to a sit-in on the House floor last year when Democrats protested the lack of gun legislation that has passed in the chamber.

“This announcement is the result of a frivolous complaint, filed by a highly partisan outside group about activities during the sit-in last year – a complaint that is without merit,” Shoemaker wrote. “Congressman Luján is committed to abiding by House Rules, is confident he has done so in this case and looks forward to a timely resolution.”

Contact Rahman at remarahman@cqrollcall.com or follow her on Twitter at @remawriter