NDP Member of Parliament Nathan Cullen is part-way through a tour of Liberal ridings across Canada to drum up support for his upcoming motion on federal electoral reform.

Despite a campaign promise to change Canada's first-past-the-post electoral system and a year-long review process conducted by a multi-partisan committee, Prime Minister Justin Trudeau said the government would not be pursuing reform.

Since then, 130,000 people have signed a petition calling for Trudeau to follow through on electoral reform.

That petition was led by Cullen, who is the MP for Skeena-Bulkley Valley in Northern B.C.

"All we're asking for him to do is keep his promise," he told CBC's The Early Edition.

Cullen plans to introduce a motion to request the House of Commons to accept the electoral reform committee's recommendations — which included a referendum on proportional representation, among other recommendations — by the end of May.

He is currently on a cross-Canada tour, visiting 20 Liberal-held ridings where he's hoping to pressure MPs to vote for his motion.

"[The committee] produced a report that said overwhelmingly that experts and Canadians are asking for a proportional voting system," he said.

"We're hoping to get enough Liberal MPs to join with us and get this whole conversation back on track so we can do something at the national level."

The 'last opportunity'

Cullen is optimistic his Liberal collegues can be persuaded to vote with him.

"What I've noticed from my Liberal colleagues is that they've never taken a vote on this. They didn't take a vote in caucus. Trudeau decided himself," he said.

"It wasn't just Justin Trudeau that made a promise [of electoral reform]. It was every Liberal that ran for office and succeeded and entered Parliament. They also promised this."

But he noted time is quickly running out if reform is to be implemented by the 2019 federal election.

"If Parliament sends the signal before summer that we're interested in changing the voting system, there's still time before the 2019 federal election in the fall," he said.

"[But] this is the last opportunity."

Listen to the interview with Nathan Cullen on CBC's The Early Edition: