The Conservative party has warned its members that a federal election campaign could start within days, in an internal letter that makes an "urgent" appeal for donations.

Despite Prime Minister Stephen Harper's assurances that he does not want an election, party heavyweights are warning supporters that anything can happen after the federal budget is tabled Monday.

"We need to be ready to campaign within the next week," said the note, sent to party members Thursday.

"Without your help, we may need to cut back on major parts of our campaign plan. That's why I'm making an urgent appeal today to our most loyal supporters."

The note by Irving Gerstein, chair of the Conservative Fund Canada, was obtained by The Canadian Press after it was erroneously sent to a former Conservative who left the party but still receives its correspondence.

Gerstein's note goes on to ask for gifts of $150 or $75 and says the party has specific plans to use the money in the first days of the campaign.

Despite the letter's urgent tone, an imminent election appears unlikely unless the Harper government engineers its own demise.

All opposition parties face obstacles in preparing for an election. Unless Harper backed off his promise of fixed election dates and unilaterally went to the Governor General seeking a fresh mandate, there could be an election only if all three opposition parties combined to vote down the minority Conservative government.

The question is: why would they want to?

The Liberals have slumping poll numbers and a new leader who's busy establishing a national organization, putting together a platform and working to improve his English.

The NDP has also seen its support drift downward and in some recent polls was either statistically tied with the seatless Green party, or just struggling to remain ahead of it.

The Bloc Quebecois would enter an election with a demoralized campaign team if the Parti Quebecois loses the March 26 provincial election and the prospect of Quebec independence again slips away.

Even if the PQ did win a majority, sovereigntists would likely be too tired after a provincial election and too busy preparing for a referendum to bother with a federal vote.

All those factors have some political insiders musing that if Harper wants an election, the only way for him to get one is to sprinkle the budget with measures his opponents could never support.

Like Harper, Dion has said he does not want an election but is also urging his troops to prepare for one.

On Friday, he said the Liberals will base their budget vote on whether it addresses three key concerns: economic competitiveness, social justice and environmental sustainability.

"We will assess what to do with this budget when we will see it," Dion said.

"We're only hoping that this budget will be everything that this last budget wasn't."

As for whether Harper wants an election, numerous opinion polls place him short of his coveted majority and he has repeatedly said he wants to continue governing.

But the letter from Gerstein suggests Tory troops are well into planning for the alternative.

Gerstein explained that he was raising funds specifically for the early days of an election campaign during which, he wrote, "advertising and outreach" will be key.

"We may have only a little time left to finalize our finances for the first few days of the upcoming election."

Gerstein's letter went on to praise Harper for his strong leadership, which he said has put the party in a good position to win the election.

"We are in a campaign readiness status right now," he said.

"There could be an election very soon. Please act now and send the most generous contribution you can today."