OTTAWA --The NDP is facing new accusations of abusing its Parliament Hill resources by running its union office out of the Opposition Leader's office in Ottawa.

“We see they’ve completely blurred the lines, using taxpayers money to fund their union operations out of their leaders office. It seems very bizarre,” said Liberal MP Dominic Leblanc.

The NDP has strong labour ties and is the only political party with unionized staff. After the party’s 2011 election breakthrough, staffing levels swelled.

More than 500 employees pay roughly $25 in union dues each paycheque, but its local union office that represents them does not pay rent.

CTV News has obtained the collective agreement between the Communications, Energy, and Paperworkers Union of Canada (CEP Local 232) and the NDP Federal Caucus. It states the NDP "Caucus will provide office space for CEP local 232," and get access to all the resources that come with it.

The CEP has since severed ties with the NDP. Employees are now represented by the United Food and Commercial Workers.

Aaron Wudrick of the Canadian Taxpayers Federation calls the arrangement “shocking.”

“The union would have office space, computers, phone lines. These are things taxpayers are on the hook for that they shouldn't be,” he said.

The powerful Board of Internal Economy has strict rules on how political offices can be used:

Section 7.2 States “A member may not use funds, goods, services and premises provided by the House of Commons for the benefit for any person, association or organization”.

Conservative MP Paul Calandra believes the NDP has breached those rules.

“It’s yet another example of really what's becoming a troubling pattern of abuse by the NDP," he said.

The NDP is currently fighting a ruling by the Board of Internal Economy to repay millions for using House of Commons resources to fund its partsian satellite offices.

Some New Democrats have long complained they were uncomfortable with a union office inside their leaders office.

“I found this fairly odd, and it’s one of the reasons that I'm glad I became an independent, then member of the Green Party,” said former NDP MP-turned Green Party MP Bruce Hyer.

But the President of the NDP’s Local Union 232, Anthony Sallom, denies its union office does partisan work. He says the office has been around for years and is used as an important resource for its unionized staff.

“We’ve got people playing partisan politics, making a mountain out of a molehill,” he said.

“At the end of the day, there's nothing exceptional, or unusual in terms of what we're doing."

But with a federal election looming, the Conservatives and Liberals want to make this an issue. Both plan to ask the board of internal economy to investigate.

With a report by CTV's Richard Madan