The NDP is telling Canada's biggest broadcasters to either get Stephen Harper into the debate or they are skipping out too.
CBC News has learned the NDP will only consider debate invitations until Friday, Aug. 7.
While the NDP did initially agree in principle to attending the consortium debate held by Canada's biggest broadcasters, it now says it will only attend that debate and any others if the prime minister is present.
The Conservatives had already declined to participate in the consortium debate saying they had received too many invitations.
The NDP has outlined a total of three criteria for participating in debates including having a non-partisan host, topics that are varied and relevant to a large number of Canadians and that the prime minister agree to attend.
The Liberals and the Green Party had also agreed to the consortium's debate proposal
Green Party Leader Elizabeth May reacted on CBC News Network's Power & Politics, saying she was "devastated" and calling the decision by the NDP leader "anti-democratic".
May says she had hoped pressure by all parties would bring Prime Minister Stephen Harper to the debate.
"But this is a tag team," said May. "It's Conservative-NDP collusion once again to keep the Greens out of the debates and I'm really disappointed."
NDP campaign chair Anne McGrath says the party is still receiving debate invitations and at some point it needs to decide on which debates leader Tom Mulcair will join.
"I don't really want to comment on people's ideas about what our motivations may or may not be, or what we are doing," McGrath said.
"I can assure you that we are making decisions on these debates based on what is in the best interest of a robust debate during the federal election campaign."
The Conservatives have taken a hard line in refusing to attend the consortium debates, and if the NDP is also out, it may lead others to reconsider their attendance.
The English-language debate is scheduled for Oct. 8 and the French debate for Oct. 7.
The NDP says it will still look to participate in an equal number of French and English debates.
The first debate is to be held on Aug. 6, and hosted by Maclean's magazine.