One of Prime Minister Stephen Harper's top aides failed to make a scheduled appearance before a Commons committee Tuesday, a day after he said cabinet staffers will no longer testify at committees.

Harper's director of communications, Dimitri Soudas, had been called to appear before an all-party committee as it investigates allegations of political interference in the release of documents under the Access to Information Act.

Speaking to CTV's Question Period Sunday, Soudas said cabinet ministers, not staffers, will only go before committees, announcing a new "government-wide" policy.

"Ministers are the ones who are accountable and answer to Parliament," Soudas said.

On Tuesday, Government House Leader Jay Hill told the House of Commons that the committee system doesn't play fair when questioning staffers. Hill said political staff will be told to decline requests to appear before committees.

"The tyranny of the opposition majority has turned its attention to the men and women who make up our political staff," said Hill.

"Men and women who did not sign up to be tried by a committee -- to be humiliated and intimidated by members of Parliament."

A number of other government staffers are now not expected to testify later this week.

Instead of Soudas, Transport Minister John Baird appeared before the committee Tuesday.

He announced that he will also appear before the government operations committee rather than his staffers.

"The days when you could call in 25-year-old young people into this committee, to beat up staff who can't defend themselves, are over," Baird said.

"He's no 25-year-old," Liberal MP Wayne Easter shot back. "He represents the Prime Minister's Office on TV every day."

"We see more of the PMO through Dimitri Soudas than ministers who have ministerial responsibility in this government."

The matter has set off a row with the opposition, who just won a hard fought victory over the release of documents relating to the Afghan detainee issue.

"The Harper government doesn't hesitate to blame political staff when they're caught carrying out the Conservative culture of deceit," Liberal House Leader Ralph Goodale said in a statement Tuesday. "Now that Parliament wants to hear from those staffers, they're trying to cover it up. Does the Prime Minster need to be reminded again that it is Parliament, not him, who decides the rules?"

Bloc Quebecois Leader Gilles Duceppe has called the government's move "just unacceptable."

The Commons ethics committee also criticized the new policy and said it wants witnesses formally summoned. A witness who ignores the summons could be found in contempt of court.

Tuesday's committee has been looking into whether Sebastien Togneri, as an aide to then-Public Works Minister Christian Paradis, pushed bureaucrats to "unrelease" a 137-page report on the government's real estate portfolio that had been approved for release to The Canadian Press.

The document was later released with 107 pages blacked out.

Baird wasn't the first minister to appear before a committee on behalf of a staffer. Last Thursday, Human Resources Minister Diane Finley surprised committee members when she appeared instead of her communications director, Ryan Sparrow. Sparrow was to address a report that he had blocked an information request by the Globe and Mail.