A Conservative MP is calling for an investigation following accusations the NDP is abusing Parliamentary resources by running its union office out of the Opposition Leader's office.

Conservative MP Randy Hoback sent a letter to the chair of the Board of Internal Economy on Thursday, asking the board to probe allegations the NDP is providing the union free office space in Ottawa.

CTV News obtained the collective agreement between 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 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 their local union office does not pay rent for its office space.

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

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”.

In his letter, Hoback called the allegations "very disturbing."

He called on the board to investigate whether the NDP had broken rules on using Parliamentary resources for non-Parliamentary purposes.

"If true, this would add to a pattern of abuse that the NDP has shown over the last few years with respect to the resources provided to them by taxpayers," he said.

The NDP is currently fighting a ruling by the BOIE to repay millions for using House of Commons resources to fund its partisan satellite offices.

Some New Democrats have long complained they were uncomfortable with a union office inside their leader's 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."

With a report by CTV's Richard Madan