At an event organized by the Canadian Labour Congress this week, Prime Minister Justin Trudeau was confronted with harsh criticism by young members of the labour organization who felt the Liberal leader had turned his back on them.

"Honour your promises!" demanded some.

This discontent on the Canadian political left is not yet a big problem for Trudeau's Liberals. They have more support today than they did on election night in 2015, much of those gains coming from past supporters of the NDP.

But as the government moves forward — or fails to — on a number of controversial files, from electoral reform to pipelines to peacekeeping, this discontent could indeed become a problem.

In addition to the progressive voters Trudeau has lured away from the NDP since the last election, a majority of Canadians who still support the New Democrats say they are "very" or "somewhat" satisfied with the outcome of last year's vote, according to a recent poll by Forum Research.

An Abacus Data poll from August found that three-quarters of Canadians who self-identified as being on the left or centre-left of the political spectrum approved of the government.

Maintain this coalition of centrist and left-wing voters and the Liberals will have an easy time winning elections. The New Democrats are now polling in the low-teens nationwide — a recipe for another Liberal majority in 2019.

But a number of issues will make it more difficult for the Liberals to hold this coalition together as the government moves from rhetoric and consultations to decision-making.

Delegates at the Canadian Labour Congress National Young Workers Summit discuss their fristartions with the Trudeau government which prompted their protest of the Prime Minister. 1:57

The electoral reform promise

Though the prime minister says he is still committed to electoral reform, the Liberals have been sounding increasingly less confident in their ability to get it done.

Electoral reform is not as important an issue to Liberal voters as it is to those who support the NDP. Forum has found while 72 per cent of NDP voters agree that the electoral system needs to change, just half of Liberal supporters do. Polling by EKOS Research has also found that New Democrats are much more likely than Liberals to feel the current system is past its due date.

The kind of reform that is adopted — if any reform is adopted at all — could also prove problematic for the Liberals. Polls show NDP voters clearly prefer a form of proportional representation (PR), whereas Liberals are more divided on whether they prefer the current first-past-the-post system, proportional representation or alternative voting. (Trudeau has previously expressed interest in ranked ballots, for example.)

Adopting alternative voting — widely perceived to be most beneficial to the Liberal Party — or failing to implement any kind of electoral reform at all could disillusion some of the progressive voters Trudeau has brought into the Liberal tent.

Peacekeeping maybe, combat maybe not

The government is currently examining where Canada could send peacekeeping troops to Africa. A decision is unlikely to be made before the end of the year. But the intensity of that mission could also cause some malaise among left-wing voters.

Forum's polling has found a majority of both Liberal and NDP supporters approve of sending peacekeeping forces to Africa, though New Democrats are somewhat less enthusiastic. But once respondents were told that these peacekeeping forces could come under fire, support plunged — particularly among New Democrats.

Prime Minister Justin Trudeau and his son, Xavier, stand in front of an honour guard as they arrive at the International Peacekeeping and Security Centre near Yavoriv, Ukraine in July 2016. (Adrian Wyld/The Canadian Press)

A majority of Liberal voters were still in favour, though disagreement increased by nine points, to 28 per cent. New Democrats were split, with 39 per cent still approving of sending peacekeeping forces to a region that could become hot, and 40 per cent disapproving.

Other foreign policy positions could complicate matters for the Liberals on their left flank and limit their potential for growth among NDP voters. A Forum poll in September found New Democrats were twice as likely as Liberals to disagree with forging closer ties with China — one of the more notable foreign policy shifts the Liberals have made since taking office.

Pipelines and carbon pricing

The issue that best encapsulates the Liberals' delicate balancing act between progressive and centrist supporters, however, is pipeline construction. This was one of the most important sources of angst among Trudeau's hecklers this week.

The prime minister gets high marks among left and centre-left voters on the issue of climate change. Abacus found that between 71 and 78 per cent of Canadians on this end of the political spectrum feel he is on the right track on the issue.

But even when coupled with a shift toward renewable energy, the building of new pipelines is met with greater opposition — particularly among those on the left.

Abacus found that 41 per cent of centre-left voters support new pipelines when coupled with a shift toward renewable energy, while another 31 per cent can accept it. About 29 per cent stand in opposition.

Among Canadians who self-identify as being on the left, however, that opposition increases to 40 per cent and support drops to 35 per cent. The 25 per cent who can accept the building of new pipelines gives Trudeau some wiggle room. But he still runs the risk of alienating between 29 to 40 per cent of voters on the left with every new pipeline approved.

On the centre and on the right, opposition was less than 20 per cent.

It's unlikely Trudeau and the Liberals will be able to maintain their high levels of support indefinitely. This week's tense confrontation with youth members of the Canadian Labour Congress served as a stark demonstration of the kind of opposition already facing them.

But as Trudeau's government spends more time governing and making decisions that will inevitably disillusion elements of its broad coalition, these demonstrations of opposition — particularly on the left — could become more and more frequent.