A parliamentary committee has determined the NDP broke the rules when it used taxpayer-funded resources to send nearly 2 million mailings to households across the country, CTV News has learned.

Calling them “information letters,” the NDP sent at least 1.8 million pieces of mail to 26 ridings using House of Commons postage.

The so-called franking privilege allows MPs to send postage-free mail to constituents, but they are prohibited from using parliamentary resources for electoral campaigning.

The mailings had the NDP logo and directed people to the party’s website. The Liberals have complained the mailings are “electoral in nature” and therefore should not have been sent out using franking privileges.

After months of investigating, the parliamentary committee that oversees House of Commons spending concluded the letters were partisan, “prepared by and for the benefit of the NDP as a political party to advance electoral purposes.”

CTV News has been told the committee will now decide whether the NDP should pay back the House of Commons -- and if so, then how much.

Sources say the NDP could be on the hook for more than $1 million.

The New Democrats were defiant Monday night, accusing the Conservatives and Liberals of turning the House of Commons’ Board of Internal Economy into a “Kangaroo court.”

“Today’s unprecedented move confirms that, under Stephen Harper’s Banana Republic Conservatives, due process and the rule of law are secondary to political gamesmanship,” the NDP said in a statement.

“Behind closed doors, with no due process and no opportunity to review the evidence, the two parties transformed the BOIE into a Kangaroo court. Ironically, this transformation is the ultimate misuse of parliamentary resources being used for partisan purposes.”

The party said it had checked with Commons administration before launching its mailing program and “undertook due diligence” to make sure it followed the rules.

Elections Canada is also investigating the NDP mailings to determine if they broke election laws.

The New Democrats have also been in hot water over their use of satellite offices in Montreal and Quebec City. Documents released last month showed that House of Commons administration had no idea that NDP staffers approved to do constituency work in Ottawa were actually working in a Montreal party office.

NDP Leader Thomas Mulcair has insisted that the party has done nothing wrong.

With a report from CTV’s Ottawa Deputy Bureau Chief Laurie Graham