Green Leader Elizabeth May says ending Canada's first-past-the-post electoral system would be her party's first priority in exercising influence in a minority Parliament.
In an interview, May said her support for the NDP or Liberals would be contingent upon them following through with promises to change the way MPs are elected.
May favours a proportional representation system that would see her party's share of the vote produce more Green members of Parliament.
In the 2011 election, the Greens captured 3.9 per cent of the national vote, and they have consistently exceeded that level in recent opinion polls.
"We want to make sure that happens — that we move to proportional representation," she said Wednesday.
The NDP has expressed support for a proportional system in which voters would cast one ballot for a local candidate and another for a party. The Liberals have promised to appoint an all-party committee to come up with recommendations on a replacement for the first-past-the-post system.
The Green leader says other conditions for her support would be repeal of the Conservative anti-terrorism bill C-51, genuine action on climate change and a much smaller role for the Prime Minister's Office in federal affairs.
The Greens had just two seats in the last Parliament but hope to expand that base in the Oct. 19 ballot as a means of swaying policy in a minority scenario.
A new electoral system would benefit the Green party, but May says the first-past-the-post model must go because it is the "source of a lot of the toxicity in politics."
The current system punishes parties that want to co-operate, since they instead adopt a winner-takes-all attitude, she said. "The greatest level of hostility and venom, really, is between parties closest to each other on the political spectrum."
May said while she would work with the NDP or Liberals, she has no plan to backstop a Conservative minority government. A key reason: she wants Harper gone before a United Nations conference on climate change set to begin in Paris on Nov. 30.
The conference's goal is a new international agreement aimed at keeping the rise in global warming below two degrees Celsius.
"These are deadline negotiations," May said. "The stakes couldn't be higher."
Federal consultations with the provinces would need to begin immediately after the election to come up with a new Canadian position for the conference, she added.
The federal anti-terrorism bill gave Canada's spy agency new powers to disrupt plots, expanded federal information-sharing and created the offence of encouraging a terrorist act. Civil libertarians and privacy advocates have strongly denounced the measures.
The NDP has promised to repeal the bill, while the Liberals — who voted for the legislation — have indicated a need for changes.
May also plans to push for a "significant shrinking" of the PMO.
"I actually find that Canadians are incredibly interested in democracy, and alarmed when they realize that the Prime Minister's Office is controlling virtually everything that goes on within the federal government."