WINNIPEG -- Manitoba's opposition parties are calling for an inquiry and the ousting of an NDP MLA from caucus after Premier Greg Selinger admitted he knew for months that a former cabinet minister misled the legislature.

Selinger told The Canadian Press he knew "early on" that former Immigration Minister Christine Melnick had likely misled the chamber in the spring of 2012, but he did not make that information public.

Manitoba's ombudsman found the assistant deputy minister of immigration was following Melnick's direction when he sent out a controversial email inviting immigration agencies to a politically charged debate in the provincial legislature.

Melnick -- who has since been dropped from cabinet -- told a legislative committee she wasn't behind the email at the time. She has repeatedly declined interview requests.

She issued a short written apology last week. "The explanation I provided in the house did not properly convey the direction I had given, and for that, I apologize," Melnick wrote.

Conservative Leader Brian Pallister said Selinger should have corrected the record as soon as he found out.

"A lie is a lie," Pallister said Wednesday. "The premier knew 18 months ago that his minister had lied about his government's attempt to involve the civil service in a partisan activity. That means that the premier was part and parcel of perpetuating the lie for a year and a half. That is just not on."

The ombudsman's investigation found the bureaucrat didn't break any laws or guidelines when he sent an email in April 2012 that invited immigrants and newcomers to come watch the NDP government debate a resolution condemning the federal Conservative government for centralizing some immigration programs.

Despite Melnick's denials, the investigation found Ben Rempel was following Melnick's direction at the time. Selinger told The Canadian Press on Tuesday he knew Melnick "may have issues with information she put on the public record" but the premier didn't want to interfere with the ombudsman's investigation.

Selinger said the ombudsman's investigation into Melnick was one of the reasons she was moved to the back benches. A spokesperson for Selinger said the premier didn't have anything to add to his comments Tuesday and isn't considering further action.

But Pallister said Melnick should face tougher consequences.

"Clearly this minister lied to the people of Manitoba, lied to her colleagues, lied to the legislature and so she should be removed from his caucus pending a full investigation to determine what should be done," Pallister said. "Claiming that he's dealt with the issue because 18 months after he knew about it, he took her out of cabinet, is just a ploy to make Manitobans believe he is a man of action."

Both Pallister and lone Liberal MLA Jon Gerrard say Selinger should appoint a legislative committee to look into the controversy. Gerrard, the former Liberal leader, said he was shocked to learn Selinger knew Melnick had instructed a senior civil servant but didn't say anything.

"Christine Melnick and the premier should have been forthright right from the start and the moment that the premier knew, he should have made sure the record was made public," Gerrard said.

"I think there is a real question now -- when did the premier know?"