New Democrat MP Nathan Cullen is planning a series of town-hall meetings in Liberal ridings across the country in an effort to resurrect the issue of electoral reform.

Prime Minister Justin Trudeau backed away in February from his election promise to end first-past-the-post voting, saying there was no consensus on a replacement system.

Cullen has tabled a petition with 130,000 signatures calling on Trudeau to keep his promise on electoral change.

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He says he will challenge 20 Liberal MPs to show up at meetings in their ridings to debate the issue.

He also says those 20 votes would make all the difference if those MPs were to break with the prime minister.

The first town hall is scheduled for Saturday in Toronto.

Cullen says an analysis of the petition shows support across the country.

"Canadians, many who voted Liberal in the last election, are rightly upset," he said today in Ottawa.

"I believe that there's no more sacred commitment or connection than the one between a prime minister who runs on a clear campaign promise and the people he seeks to represent."

There is one chance to salvage the reform process – when the electoral reform committee's report comes up for a vote in the House of Commons in May.

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"This will be the last opportunity for the Liberals to do the right thing," he said, "to follow through on the campaign commitment ... and bring in a voting system where, truly, every vote can count."