The Conservative government has presented a new cabinet policy directing that only cabinet ministers and not their political staff can appear as witnesses before parliamentary committees.

Government House leader Jay Hill says testifying at parliamentary committees is the responsibility of cabinet ministers and not their staff. (Adrian Wyld/Canadian Press)

The controversial new policy could trigger a fresh showdown between Prime Minister Stephen Harper and the opposition parties over the powers of Parliament, just weeks after a similar dispute over MPs' access to uncensored documents pertaining to Afghan detainee transfers was resolved.

In a statement in the House of Commons on Tuesday morning, government House leader Jay Hill blamed the "tyranny of the opposition majority" for turning its attention to government staffers "who did not sign up … to be humiliated and intimidated by members of Parliament."

He said the new policy ensures "there is no substitute for ministerial responsibility."

"It is ministers who decide policy and ministers who must defend it before the House and ultimately before the people of Canada," Hill told the House. "Public servants and staff support ministers' authority; they do not supplant it."

In response to Hill's statement, Liberal House leader Ralph Goodale said the Conservatives have introduced another policy that is "about secrecy, about preventing accountability, about stifling transparency, about muzzling" all of the government's assistants.

"The arrogance and the hypocrisy of this position are breathtaking," he said. "Parliament has the power to call any and all witnesses. The government and its ministries are responsible to Parliament, not the other way around."

During Tuesday's question period, NDP Leader Jack Layton accused the Conservatives of deliberately shielding staffers who interfered with access-to-information requests for political purposes.

"Why does the prime minister want to hide employees who put in place directives to hide the truth?" he told the House.

Harper replied the precedents and practices are clear that staff are accountable to the ministers, who are in turn responsible to the House and its committees.

"When there is a question about conduct in a minister's office, the committee obviously can call ministers, and ministers will answer those questions," he said.

Staffers 'humiliated and intimidated' by MPs: Soudas

The new policy comes as Harper's spokesman, Dimitri Soudas, declined a request to appear before the all-party committee of MPs as they investigate allegations of political interference in the release of documents under the Access to Information Act.

Transport Minister John Baird waits to testify before the Commons ethics committee on Parliament Hill in Ottawa Tuesday. ((Sean Kilpatrick/Canadian Press))

Soudas said the guiding constitutional principle in Canada is ministerial responsibility, not staffers', and that he wouldn't show. He told CBC News that opposition MPs are using the committees to conduct "random interrogations without due process or any rules of fairness."

"It's one thing for politicians to be tough on each other," Soudas said. "But we draw the line when people who aren't elected, like ministerial staff, are humiliated and intimidated by members of Parliament."

Transport Minister John Baird appeared in Soudas's place on Tuesday. Baird and Conservative MPs on the committee reiterated the government's position that testifying at committees is a ministerial responsibility.

But NDP MP and committee member Bill Siksay said he would table a motion to summon Soudas at the committee's next meeting.