Federal New Democrats will not heed calls from the Green Party of Canada asking the NDP not to run a candidate in the Labrador riding vacated by former Conservative cabinet minister Peter Penashue.

"If someone should stand down in this byelection it is Peter Penashue while Elections Canada completes its investigation," said NDP National Director Nathan Rotman in an email to CBC News on Sunday.

Green Party leader Elizabeth May had announced Saturday that the Greens would not be running a candidate in an upcoming Labrador byelection and urged the NDP to follow suit.

May said such co-operation would rally the progressive vote behind the Liberals and encourage proportional representation.

Liberal leadership candidate Joyce Murray took credit for the Greens not running a candidate in Labrador, in a news release issued on Saturday, saying she called May and asked her not to.

Federal Liberal leadership frontrunner Justin Trudeau welcomed the decision by the Greens while pouring scorn on Murray's co-operation proposal, during an exchange with Murray at the last leadership debate in Montreal on Saturday.

"I encourage all members of the Green party to vote for the Liberal party, in Labrador and across the country," Trudeau said.

Murray fired back saying her proposal of political co-operation was an "insurance policy" to defeat the Conservatives in 2015.

However, NDP leader Tom Mulcair has flatly rejected the idea of political co-operation with the Liberals.

Said Rotman: "The NDP respects the right of Canadians to make a democratic choice — and will ensure they have an opportunity to vote NDP, if they so choose."

Penashue says he will run in byelection

Penashue quit his post earlier this month after Elections Canada found his election campaign had accepted 28 different ineligible donations.

He has since pledged to run in a byelection, and is being supported by Prime Minister Stephen Harper, even though Elections Canada is continuing to investigate.

Elections Canada documents show that almost $48,000 in improper donations have been repaid to the federal Receiver General.

So far, only one candidate is seeking the Liberal nomination in Labrador.

Yvonne Jones, a former leader of Newfoundland and Labrador's Liberal Party, declared her intention to run for the Liberal nomination in Labrador on the heels of Penashue's resignation. However, Todd Russell, the former Liberal MP whom Penashue defeated by 79 votes in 2011, is expected to announce his intentions on Monday.

Harry Borlase will represent  the NDP in Labrador, Rotman confirmed Sunday.

Borlase obtained a bachelor’s degree in political science and Canadian studies from Mount Allison University and completed a master of arts in polar law in Iceland before returning to Newfoundland and Labrador to work for Memorial University on a climate change project focused on Labrador.

Earlier this week, Harper led a spirited defence of the ex-intergovernmental affairs minister in the House of Commons.

Harper has at least 11 days and no more than 180 days to call a byelection from the date of March 18 when the chief electoral officer received the notice of vacancy for Labrador.

That means the earliest Harper could call a byelection is on March 29.

With files from The Canadian Press