OTTAWA - MPs moonlighting on the public dime should at the very least return a portion of their hefty salaries if their second careers conflict with their parliamentary duties, says a watchdog group.

The Canadian Taxpayers Federation says that when Parliament is in session MPs have a duty to represent their constituents and not tour the country to line their pockets with a second income. MPs earn $158,000 annually plus other perks and benefits

The issue has come to the fore after self-confessed millionaire and leadership candidate Justin Trudeau padded his bank account on the speaker's circuit.

Since becoming a Liberal MP in 2008, Trudeau has socked away nearly $280,000 in fees he charged schools, unions and others to hear him yammer - on top of hundreds of thousands of other dollars he banked before becoming an MP.

"If Mr. Trudeau, or any other MP, is away on private business then they ought to have their parliamentary pay docked," Gregory Thomas, the federation's national director, said Wednesday.

"When the House is actually sitting - which isn't that much - that's where they should be. That's what we're paying them to do - study, debate, and vote on legislation before Parliament."

Trudeau was in Quebec Wednesday and - as he's done since reports surfaced about his double-dipping - refused to answer questions about his money-making sideline, including accepting $20,000 from the Ontario Public Service Employees Union. Trudeau bolted when he learned Sun News Network was asking the questions, including whether he has accepted any other union money.