NDP House Leader Nathan Cullen said the New Democrats will take to Twitter to ask questions on behalf of Canadians, "questions this government seeks to avoid."
"Questions of accountability, questions on our economy, questions on foreign affairs," Cullen said.
Cullen said party critics will tweet the questions they would have asked the government if the House of Commons were sitting this week.
MPs were scheduled to return to Ottawa today but on Friday, Harper officially prorogued the Fall sitting until Oct. 16.
Mulcair told reporters gathered in the foyer of the House of Commons Monday that Harper's decision shows "his disdain" for Parliament.
Mulcair was also asked about Quebec's proposed charter of values. He called the plan "patently illegal."
Liberal Leader Justin Trudeau has said Liberal MPs will return to work as scheduled.
On Monday, Liberals convened a roundtable on the future of the wireless industry with MPs and stakeholders.