But Liberal Francis Scarpaleggia says Mulcair and his party are getting ahead of themselves.
"He's not about to be in the position to be making the decisions," said Scarpaleggia after Question Period Thursday.
The Liberal M.P. says he doubts what action Mulcair would take if he were in that position, but says that refusing to appoint senators is "not particularly responsible"
"The answer is not to empty the place, but to make excellent appointments," he added. A leader in that situation, says Scarpaleggia, should make the best appointments possible, with the help of a vetting procedure, until reform is possible.
Constitutionally there would be nothing forcing Mulcair to appoint individuals to the Red Chamber, if he becomes the next prime minister. However, University of Ottawa Professor Errol Mendes said there are many unwritten rules that could get a leader into "constitutional trouble."
"If no senators are appointed from the Atlantic provinces or indeed other regions of the country, the unwritten principles relating to federalism and minorities enunciated by the Supreme Court in the Quebec Secession Reference could be triggered to prevent the closing down of the Senate."
Since Harper was elected in 2007, 53 senators have been appointed. Starving the Senate, or refusing to fill vacancies as they become available, could delay or halt the government's ability to pass legislation. But Julian said he doubts opposition senators would gang-up up on them, and prevent work from getting done.
"I would expect that senators would understand that there is a tide of public opinion running against them because of the scandals we've seen over the last few weeks and the fact that Canadians implicitly understand that an undemocratic nominated upper chamber that is inhabited by partisan nominations is not appropriate for a vigorous democracy that we want to have in this country."
The Conservatives and Liberals struck down a non-binding NDP motion Wednesday night to begin negotiations with the provinces. The motion was defeated 186-101.