Conservative Senator Carolyn Stewart Olsen is leaving the Senate subcommittee that was responsible for a series of controversial audits of senators' expense claims.

The development comes as the Senate prepares for a second day of contentious debate on motions to suspend Senators Mike Duffy, Patrick Brazeau and Pamela Wallin from the Red Chamber without pay. Mr. Duffy and Mr. Brazeau spoke in their own defence Tuesday, while Ms. Wallin is expected to have an opportunity to address the Senate on Wednesday afternoon. All three senators were appointed by Prime Minister Stephen Harper.

Ms. Stewart Olsen was part of a three-member steering committee in charge of the Senate committee on the internal economy. The group came under scrutiny earlier this year for its handling of a report on Mr. Duffy's housing expenses, which excluded more negative passages that were used in two other senators' reports.

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Both Ms. Stewart Olsen and David Tkachuk, the former chair of the subcommittee, have said the phrasing was removed because Mr. Duffy had already repaid the money at the time the reports were released, while former Conservative Mr. Brazeau and former Liberal Senator Mac Harb had not. Mr. Harb has since resigned.

All three senators facing the suspension motions were present when the debate began on Tuesday afternoon.

Several Liberal and Conservative senators have spoken out against the proposed suspensions, saying they are concerned the senators in question will not have an adequate opportunity to defend themselves. All senators will be allowed to vote according to their consciences on the matter, the Senate Conservative and Liberal leaders have said.

On Tuesday night, Mr. Duffy accused the Prime Minister's Office of pushing a deal on him to repay $90,000 in questionable expenses during the debate on the proposed suspensions. He also said he was threatened at one point with the possibility that Ms. Stewart Olsen and Mr. Tkachuk would help remove him from the Senate if he did not repay the money – an allegation both deny.

Asked if the current controversy and Mr. Duffy's allegations played a role in her decision to leave the committee, Ms. Stewart Olsen acknowledged in an e-mail to The Globe and Mail that "it has been a difficult time" and she would like a change, but said she was also interested in turning her focus to other matters.

"I have been on the committee for some time and we have made rule changes and that was a goal for me," Ms. Stewart Olsen wrote. "More has to be done of course, but it will happen [because] we are committed to transparency and change. I want to be able to devote more time to my province and to work on regional issues."

Ms. Stewart Olsen is a former press secretary to Mr. Harper who was appointed to the Senate in 2009. She said she does not know who will replace her on the committee.

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Ms. Stewart Olsen has a long and close association with Mr. Harper. Dating back to Mr. Harper's time as Opposition Leader, she and Ray Novak – who is now the Prime Minister's chief of staff – appeared to be at Mr. Harper's side at all times. Shuttling across the country to attend events with the leader, they would be the ones riding in the back seat with Mr. Harper. The two have likely spent more private time with Mr. Harper than any other political staffer during his years as party leader.

With files from Bill Curry