The Conservative MP embroiled in a taping scandal will be taking an indefinite stress leave, but he will not be leaving the Tory caucus, party leader Stephen Harper confirmed Monday.

"Earlier today, Newton-North Delta MP Gurmant Grewal informed me in writing that he would be stepping down from his position as co-chair of the Standing Joint Committee for the Scrutiny of Regulations, while the current investigation takes place," Harper said in a written statement.

"I look forward to Gurmant reassuming these responsibilities when these matters are resolved."

In addition, the Tory leader said that he has been aware that Grewal has been feeling "significant personal pressure."

"As a result, he and I agreed that he should take a temporary stress leave from his parliamentary responsibilities," Harper said.

Conservatives met Monday to make a decision on Grewal's fate within the party after Air Canada officials confirmed they are investigating the MP over an incident involving a package, CTV's Ottawa bureau chief Bob Fife reported.

"There was speculation that he would be asked to step out of the Conservative caucus over this Air Canada incident," Fife reported.

Grewal allegedly went to an Air Canada ticket agent to ask if someone could carry a package to Ottawa on Saturday.

According to reports, a union official told him this was a security violation.

The official then said Grewal booked himself on the flight and passed through security to a waiting area, where he allegedly asked other agents if they could provide him with a list of politicians who would be on the plane, and said he wanted one to transport the package.

He was reportedly told again this was impossible because of security practices but was apparently successful in finding someone to take the envelope to Ottawa.

"We can confirm that we are currently investigating an incident involving Mr. Grewal," said Air Canada spokeswoman Laura Cooke, but would not confirm whether there was a tape in the envelope.

Meanwhile, Grewal told CTV News that the allegation is false.

The investigation comes as the controversy over tape-recorded conversations between Grewal and two high-ranking Liberals shows no signs of dying down on Parliament Hill.

Liberals continued to be hammered by Bloc Quebecois members during Monday's question period over whether Prime Minister Paul Martin knew what was going on during the negotiations.

"Was the prime minister made aware by (his chief of staff Tim) Murphy that a member wanted to sell his vote? That is the question, I am allowed to put it, and he has a duty to answer," Bloc Quebecois Leader Gilles Duceppe asked Monday, appearing increasingly flustered as he reworded the same question several times.

The Liberals, however, reasserted their position that they could not directly respond to the question.

"The member is basing his question on tapes that have been proven by many audio experts to have been manipulated," Liberal House Leader Tony Valeri said.

Conservative MP Gurmant Grewal claims he and his wife, Nina, were offered plum positions in exchange for voting with the Liberals in a crucial budget confidence vote on May 19.

He says he has proof of that in tape recordings, recently released to the public.

However, the Liberals said that there were conversations missing from the transcripts of the tapes. The Liberals also accused the Conservatives of altering the tapes.

There is word today that the tapes may have been altered -- that from a forensic audio expert employed by The Globe and Mail. And the expert says it's unlikely the changes were caused by digital copying, as the Conservatives say.

A new version of the transcripts was released last Thursday, and the party issued a press release saying "brief passages" had inadvertently been cut when the recordings were transferred from master digital files to compact discs.

U.S. forensic expert Jack Mitchell told The Globe that the tapes had definitely been edited. He said one telltale sign was the repetition of a brief snippet of conversation.

"The entire thing repeats exactly. It's not the speaker repeating his phrase," he told The Globe.

"This repeats exactly in the same way, with the same rhythm, with the same timing, with the same noise signatures. This is impossible."

However, Mitchell could not say how the alterations occurred, or if they were done intentionally.

There are several people overheard on the tapes, including Murphy and federal Health Minister Ujjal Dosanjh.