The opposition parties are calling for parliamentary committee hearings into “the political operations of government departments” after partisan letters written by a Conservative cabinet minister were posted to a federal government website.

The two letters were written by International Co-operation Minister Julian Fantino, who is responsible for the Canadian International Development Agency (CIDA), and posted to the department’s website. The letters were originally written to publications in response to published commentary by opposition critics.

On Wednesday, Liberal MP and former cabinet minister John McCallum wrote to NDP MP Pat Martin, chair of the House Government Operations Committee, and suggested that a sub-committee be formed to hold hearings on the issue, so as not to over-burden the committee’s workload.

“It is clear that Parliamentarians may have a different understanding of what constitutes ‘political activity’ by departments than what the rules allow,” McCallum, his party’s Treasury Board critic, wrote to Martin. “It is essential that Parliamentarians be informed of the rules and be provided with an opportunity to make suggestions for their improvement.”

McCallum said government officials could appear at the hearings to “explain the different legal, regulatory and policy frameworks that govern the political operations of the government. The sub-committee can then report back on the matter to the Standing Committee.”

NDP Leader Thomas Mulcair also called for a committee hearing, saying the posting of the letters were “a clear breach of the rules.”

Mulcair told CTV’s Power Play: “This is a government website, this is government property, and he’s using it for a very sharp, shrill, partisan political attack.”

In one letter, entitled “Dear NDP: CIDA Does Not Need Your Economic Advice,” Fantino criticizes the opposition’s position on international development.

“Development is not about dependency; it is about helping those in need get a leg up so they can prosper. This is a concept that the tax-and-spend NDP fundamentally do not understand,” Fantino wrote.

“While the NDP would prefer to fund endless talk shops, I am committed to ensuring our development assistance is accountable, transparent and results-focused.”

The other letter compared the current Conservative government’s record on international development with that of the previous Liberal government.

The letters caused a brief firestorm to break out over Twitter Tuesday afternoon, with several experts observing they appear to violate rules aimed at ensuring government communications remain non-partisan.

A spokesman for Fantino told The Canadian Press on Wednesday that the posting of the letters "was a genuine mistake” and that CIDA had been asked to take them down.

Andrew Frenette, CIDA’s director general of communications, said the letters were posted in error as part of a department communications push, which included posting a large quantity of material online.

“The volume was quite significant and it was like a machine, they just posted these things,” Frenette told CP. “It's quite regrettable; should never, ever have happened."

Mulcair accused the Conservatives of “a constant pattern of behaviour” in blaming staff for mistakes, saying the minister should take responsibility.

Conservative ministers have come under fire for similar errors. In 2011, the opposition called for Immigration Minister Jason Kenney to step down after his MP letterhead was used to solicit Conservative Party donations. Kenney said a staff member used the wrong letterhead, which he failed to notice because he was travelling overseas.

“Where’s the notion of ministerial responsibility? That’s the basic fundamental rule of our government,” Mulcair said. “You’re the minister, you’re in charge, you take the hit.”