Wrangling in Parliament over a possible ban on hunting with dogs is entering what could be its final week.
Hunt supporters are planning civil disobedience against a ban
Peers are on Monday expected to vote for hunting to be licensed in England and Wales from December 2007.
But they could force any ban to come into force before the next election in an attempt to rattle ministers.
MPs are set to insist on a total ban when they debate the issue on Tuesday. If there is no deal by Thursday, the ban could be forced into law.
Tony Blair's official spokesman stressed there would be a free vote among Labour MPs.
"The prime minister remains firmly committed to getting a compromise," he said.
The years of debate over a possible hunting ban could end with a "ping-pong" battle between the Lords and Commons this week.
The Parliament Act can be used to override peers' opposition if they try to thwart the will of MPs.
Commons Speaker Michael Martin is expected to say the conditions needed for the act to be used have been met if there is no agreement before this session of Parliament ends on Thursday.
But the Parliament Act cannot be used to push through MPs' suggestion that a ban be delayed until July 2006 to allow time for hunts to adapt.
Some pro-hunt peers are proposing what is being dubbed the "kamikaze" option of rejecting any delay so a ban would be enacted within three months.
With hunt supporters planning a campaign of civil disobedience, they believe bringing in a ban quickly could embarrass the government before the general election.
Baroness Mallalieu, Labour peer and president of the pro-hunt Countryside Alliance president, said:
"There is a mood in the countryside that if we are going to be banned, get on
"There is no rationale for the 18 months anyway. If something is wrong you stop it straightaway. If it is not wrong you don't
stop it at all."
Lord Donoughue, a former Labour minister, said delaying any ban simply allowed the government "to wriggle out of facing the
consequences of its policies during the election campaign".
Rural Affairs Minister Alun Michael last week appealed for peers to accept a compromise where deer hunting and hare coursing where ban and licensed fox-hunts allowed if they met "utility" and "cruelty" tests.
Such a deal could possibly stave off the use of the Parliament Act, he suggested. Downing Street also says the prime minister backs Mr Michael's proposal.
But Douglas Batchelor, from the League Against Cruel Sports, said there could be no compromise.
He told BBC News: "What MPs have decided is that the ritual practice of chasing animals with
dogs across the countryside and then killing them with dogs is cruel, is
unnecessary and should be banned.
"And I think that is what will happen this
Mr Batchelor said there was no logic in delaying implementation of a ban.