In a question of privilege put to the upper chamber Tuesday, Liberal Sen. James Cowan said Canadians "should not be fearful of telling the truth before us."
Senate Speaker Noel Kinsella is expected to rule on the matter Wednesday.
The controversy was sparked by claims that Cpl. Roland Beaulieu, currently on stress leave from the national police force, was discouraged from appearing before a committee Monday studying a bill that would give RCMP managers more power to deal with disciplinary issues.
The Mounted Police Professional Association of Canada, which represents many regular and civilian Mounties, says the RCMP told Beaulieu if he was well enough to go to Ottawa to testify, he should be fit enough to work.
Rob Creasser, a former RCMP officer and spokesman for the association, said the force had not previously objected to Beaulieu travelling outside his district of duty.
"They didn't seem to have problems with him going to other locations for other reasons," Creasser said. "I just find the timing suspect, let's put it that way."
Beaulieu, who is involved with the professional association, did not go to Ottawa — though another representative of the group did testify at the Senate's national security and defence committee.
During the House of Commons question period Tuesday, NDP public safety critic Randall Garrison accused the government of silencing Beaulieu.
"What is this minister afraid of?" Garrison asked. "Why is he muzzling RCMP officers who want to speak out on the reform of their organization?"
Some RCMP members and the NDP oppose the bill intended to modernize the force, saying it would give the commissioner too much unchecked power over rank-and-file officers.
Public Safety Minister Vic Toews said Beaulieu "indicated that he wanted to testify, and there was nothing stopping that officer from testifying."
The RCMP had no comment on the matter Tuesday.
In his remarks to colleagues, Cowan said witnesses "who wish to appear before us should not be subject to intimidation."
Cowan said he found it ironic that the senators would soon be studying another bill involving the police force, dealing with witness protection and safeguards for those who testify in courts of law.
"But what about Canadians who would like to testify before Parliament, is there to be no protection for them?"
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