OTTAWA - Justin Trudeau is reminding senators that they're unelected and have no business rewriting a federal budget passed by the elected House of Commons.

The prime minister says he respects the role senators play in providing sober second thought to legislation.

Indeed, having instigated a new appointment process aimed at making the Senate more independent and less partisan, Trudeau says he actually encourages senators to scrutinize legislation and recommend improvements.

But he's drawing a line when it comes to the government's budget implementation bill, as senators debate whether to hive off the portion of it which deals with creation of a new infrastructure bank.

Trudeau says senators need to remember that the House of Commons has authority over budgetary matters.

He's apparently referring to the fact that the Constitution prohibits the Senate from initiating a money bill; that power rests solely with the Commons.