The NDP is calling on the RCMP to launch an investigation into a $90,000 cheque former chief of staff Nigel Wright wrote to Sen. Mike Duffy.

At a press conference Monday afternoon, New Democrat ethics critic Charlie Angus said he has written to RCMP Commissioner Robert Paulson, requesting an investigation.

“I am concerned that such acts may violate the laws that the RCMP is charged with upholding and enforcing. I request that the RCMP take these concerns into account, investigate promptly and take all appropriate action," Angus writes in the letter.

Angus said that while Wright has resigned from his post, many questions still remain.

Duffy is one of three senators whose expense claims are under scrutiny over allegations they were improperly claiming tens of thousands of dollars in living expenses.

Angus also questioned Prime Minister Stephen Harper’s role in the scandal, asking why the leader says he was unaware of the $90,000.

Wright said in a statement Sunday that he did not advise the prime minister of the “means by which Sen. Duffy’s expenses were repaid, either before or after the fact.”