Opposition Leader Victor Boudreau said the premier must take swift action against Paul Robichaud because of the criminal investigation. (CBC)

Opposition Leader Victor Boudreau is calling for the resignation of Deputy Premier Paul Robichaud until the conclusion of a RCMP investigation into alleged political interference in a criminal matter involving his brother.

Boudreau raised the allegations during question period on Tuesday.

He said the Opposition has received confirmation from the RCMP that the police have started a criminal investigation into a complaint that Robichaud interfered with the prosecution against his brother for alleged aquaculture violations.

Fisheries charges were eventually laid against Robichaud's brother and are still before the courts.

Deputy Premier Paul Robichaud has been anonymously accused of interfering in a criminal matter involving his brother. (CBC)

Boudreau said he received an anonymous letter at his riding office, which suggests Robichaud pressured staff at the fisheries department not to prosecute his brother under the Aquaculture Act.

"These are allegations only. We felt it was important to let the RCMP see this letter," Boudreau said.

The Liberals passed the anonymous allegations against Robichaud on to the RCMP and received a letter on Tuesday from assistant commissioner Wayne Lang, the senior officer in New Brunswick, saying the police would investigate.

"In light of this, will the premier ask the deputy premier to step down pending the outcome of this criminal investigation?" Boudreau asked inside the legislature.

"I ask, will the premier confirm here today that he is prepared to either force or ask the deputy premier to step aside from his cabinet responsibility so long as this criminal investigation is underway by the RCMP?"

Boudreau said the premier must take swift action against Robichaud because of the criminal investigation.

Premier takes question 'under advisement'

Premier David Alward said he would take the question under advisement and would respond at a later date.

Robichaud didn't speak to reporters.

But Attorney-General Marie-Claude Blais said decisions about the laying of charges are made at arm's length from politicians.

"We take decisions as government, but they are not decisions to move forward with the prosecution of an individual.That is done by the director of public prosecutions and the power that rests with public prosecutions," she said.

"That means the attorney general doesn't decide if we pursue or not a person within the province. It is that independence that exists."

Blais said she wasn't aware of the allegations against her cabinet colleague before Tuesday's sitting of the legislature.

The letter from the RCMP does not suggest there is any proof supporting the allegations against Robichaud.

RCMP spokeswoman Const. Chantal Farrah told CBC News launching an investigation does not mean there is any evidence of wrongdoing by Robichaud.

There have been no charges against Robichaud and nothing has been proven in court.