OTTAWA -- Prime Minister Justin Trudeau is abandoning his long-held promise to change the way Canadians vote in federal elections -- an about-face his opposition rivals angrily characterized Wednesday as a cynical betrayal of trust.

In a mandate letter for newly appointed Democratic Institutions Minister Karina Gould, Trudeau makes it clear that electoral reform -- once top of mind for the Liberal government -- is no longer on the agenda.

"Changing the electoral system will not be in your mandate," the prime minister writes in the letter, released Wednesday.

A variety of consultations across the country have shown that Canadians are not clamouring for a change in the way they choose their federal government, the letter continues. It also rules out the possibility of a national referendum.

"A clear preference for a new electoral system, let alone a consensus, has not emerged," Trudeau writes. "Furthermore, without a clear preference or a clear question, a referendum would not be in Canada's interest."

Gould repeated the message in a news conference outside the House of Commons.

"If we were to change the electoral system, something as foundational as how we decide to govern ourselves, that we need to do it with the support of Canadians," she said.

Trudeau repeatedly promised -- both as a campaigning Liberal leader and as prime minister in a speech from the throne -- to get rid of the current first-past-the-post voting system in time for the 2019 federal election.

New Democrat MP Nathan Cullen, the party's democratic reform critic, savaged Trudeau as a "liar" during a news conference in the foyer of the House of Commons.

"This is one of the most cynical displays of self-serving politics this government has yet to engage in," Cullen said, accusing the Liberals of "seeking any excuse, however weak, however absent, to justify that lie to Canadians."

Trudeau, he added, "promised to conduct himself with honour and integrity.... It puts into question any promise, any commitment Mr. Trudeau makes or has made in the past."

Green party Leader Elizabeth May said she felt betrayed, noting that many members of her party had urged people to vote strategically -- in favour of the Liberals -- based on their promise to bring in electoral reform.

"I feel more deeply shocked and betrayed by my government today than on any day of my adult life," she said.

Canadians made their views known through the House of Commons special committee on electoral reform, town halls held by MPs from all parties, the travels of former minister Maryam Monsef and a much-maligned online survey called MyDemocracy.ca.

According to the mandate letter, Trudeau did not believe those consultations have produced their desired -- albeit undefined -- level of support for electoral reform, let alone any clarity on a preferred replacement.

The New Democrats, long supporters of a system of proportional representation, went into a meeting with Gould on Tuesday hoping to hear the new minister repeat Trudeau's original, unequivocal promise: that the 2015 vote would be Canada's last under first-past-the-post.

There are also some big new items in the mandate letter.

Trudeau wants Gould, Defence Minister Harjit Sajjan and Public Safety Minister Ralph Goodale to come up with ways to defend the Canadian political system against cyberthreats and hackers -- a possible consequence of the "voter fraud" and hacked email controversies emanating from the raucous U.S. election.

"This should include asking the Communications Security Establishment (CSE) to analyze risks to Canada's political and electoral activities from hackers, and to release this assessment publicly," he writes.

He also wants the three ministers to ask the CSE to "offer advice" to Elections Canada and political parties -- including opposition parties -- on "best practices" regarding cybersecurity.

The letter also asks Gould to take the lead on developing legislation to bring stricter rules -- and greater transparency -- to political fundraising, a response to months of negative headlines about so-called cash-for-access Liberal fundraisers.

The promised legislation would require cabinet ministers, party leaders and leadership candidates to publicly advertise their fundraisers in advance, and release a report after the fact with details of the event.

The proposed new law, if passed, would also require events to take place in publicly available spaces, a move designed to address concerns about well-heeled donors bending the ears of cabinet ministers in private homes.

"Other measures may follow after discussion with the other political parties," Trudeau writes.

The letter also repeats earlier commitments, such as repealing some elements of the previous Conservative government's Fair Elections Act and exploring the idea of an independent commissioner to organize leaders' debates during federal elections.

It also includes reviewing campaign spending limits and working with Treasury Board President Scott Brison and Justice Minister Jody Wilson-Raybould to increase the openness of government, including reviewing the Access to Information Act.