Elections Canada has announced the date of the federal byelection for the Ontario riding of Leeds–Grenville–Thousand Islands and Rideau Lakes.

The byelection — set for Monday, Dec. 3. — will fill the seat left vacant after the death of longtime Conservative MP Gord Brown, who passed away suddenly after suffering a heart attack in his Parliament Hill office in May.

The government had until Tuesday to announce the date.

Other ridings across the country remain without representation in the House of Commons. This includes former NDP leader Tom Mulcair's Quebec seat in Outremont and Ontario's York-Simcoe seat, up for grabs after the Sept. 30 retirement of Conservative MP Peter Van Loan, the former government House Leader under Stephen Harper.

British Columbia's Burnaby South riding is also in need of another MP after the NDP's Kennedy Stewart left the Commons for a successful run for mayor of Vancouver.

That B.C. seat will be watched closely by all parties, as the current federal NDP leader Jagmeet Singh has announced his intentions to run in that riding. Singh, a former Ontario MPP, does not currently have a seat in the Green Chamber.

Byelections in those three ridings could be delayed until early next year, but the NDP is particularly sour the prime minister failed to announce a date for the B.C. race on Sunday.

"Folks in Burnaby want to have their say," NDP MP Peter Julian — who was in the riding — told CBC News, calling the move "petty and manipulative."

Watch Jagmeet Singh discuss the byelection decision on Power & Politics

'If you can call one of the byelections, why not call the other ones?,' asks the NDP leader. 9:43

Singh also weighed in on the issue, saying the prime minister is ignoring the voices of Canadians.

Prime Minister Trudeau just decided that over 300,000 Canadians in <a href="https://twitter.com/hashtag/BurnabySouth?src=hash&ref_src=twsrc%5Etfw">#BurnabySouth</a>, <a href="https://twitter.com/hashtag/Outremont?src=hash&ref_src=twsrc%5Etfw">#Outremont</a> & <a href="https://twitter.com/hashtag/YorkSimcoe?src=hash&ref_src=twsrc%5Etfw">#YorkSimcoe</a> don’t deserve a voice in Parliament. Why? <a href="https://t.co/F4IvLBVW4T">https://t.co/F4IvLBVW4T</a> —@theJagmeetSingh

The party is calling for Justin Trudeau to announce the other three byelections immediately.

The Trudeau government attributed the singular election announcement to the length of time Gord Brown's seat has been empty.

"The deadline for the by-election called today is the end of this month, and the others were only vacated more recently. Announcements for the remaining by-elections will be made in due course," an official said in an email.

According to the CBC's Poll Tracker, an aggregation of all publicly available polling data, the Liberals lead with 37.3 per cent support nationwide, putting them four percentage points ahead of the Conservatives, who trail with 33.1 per cent.

The New Democrats find themselves stuck in third place with 15.5 per cent support, followed by the Greens at seven per cent and the Bloc Québécois at 3.9 per cent.