OTTAWA — Jack Layton says he has no "bottom line" over what has to be in the federal budget to ensure NDP support and avoid an election -- but he faces calls from his caucus to play hardball on corporate taxes.

During a break in the party's winter caucus retreat, Layton said he has put forward a list of proposals that he wants to see in the budget, and is waiting for some kind of response from the Harper government.

But he said there is no make-or-break issue that would lead the NDP to either support or reject the budget, expected in March.

"We'll look at the full budget and see what it contains," Layton said.

He is looking for a $700-million increase in the guaranteed income supplement for seniors, a more generous Canada Pension Plan, the elimination of federal sales tax on home heating, and the replenishment of funds for environmental upgrades to homes.

"We've laid these ideas out there, and we'll see what the government does by way of response," Layton said.

But finance critic and deputy leader Thomas Mulcair is more categorical. He says he and the caucus would have a lot of trouble supporting a budget that did not put a halt to planned corporate tax cuts.

"It's highly unlikely that our caucus would support a budget that continued with those across-the-board tax cuts," Mulcair said in an interview.

The corporate tax cuts are being phased in over several years, and were first included in the 2007 budget, which passed because of Liberal support.

The tax cuts won't reappear in this spring's budget unless the Tories decide they want to change direction -- something they've indicated they won't do.

Layton is also calling on the Conservatives to cancel the multibillion-dollar stealth fighter purchase and to open a national debate on defence policy.

And on funding for the Quebec City arena, Layton says he supports federal infrastructure funding for large projects in principle, but does not think Ottawa has any business supporting a sports team.