A bill to ban hunting with dogs could be delayed if calls for an outright ban are agreed, Commons Leader Peter Hain has warned.
The chase will have to be as short as possible
The Commons is due to debate the issue on Monday, with anti-hunting MPs preparing to push through amendments to enforce an outright ban.
The government is proposing a "middle way" with strict licences for remaining hunts.
Commons leader Peter Hain warned MPs on Thursday that if calls for a outright ban are agreed, there is a possibility that the bill will not reach the House of Lords - where it is likely to receive a rocky ride - before the MPs' long summer recess.
Mr Hain, an opponent of hunting, says he has been advised that if that happened, the bill would then have to go back into committee, thus delaying its passage to the Lords.
"That amended bill would obviously then have to go to report and third reading.
"Whether it's possible to get it into the Lords before the recess remains doubtful because of that," he told MPs during questions on forthcoming parliamentary business.
Labour's Kevin Hughes also warned that changes to the bill would slow it down.
"There will be enormous difficulties if substantial amendments, such as a total ban are to be agreed. It does dramatically change the bill out of all proportion," he said.
Mr Hain has already hinted that if the Lords block the bill, the government may be forced to use the Parliament Act to ensure it becomes law.
Earlier comments by Rural Affairs Minister Alun Michael about government amendments to the bill were welcomed by anti-hunt campaigners.
He said hunting should only be allowed for the specific purpose of pest control - and only after this is proved necessary and the least cruel means of doing it.
This bill will eliminate cruelty in hunting with dogs - it means the end of the prolonged chase and killing of wild animals just for sport
Rural Affairs Minister
The League Against Cruel Sports said government statement, as well as an amendment from Labour backbenchers on the bill, meant "the days of hunting are clearly numbered".
The changes to the bill include ensuring the actual chase in fox hunts is kept as short as possible and dogs in all registered hunting are kept under close control to guarantee humane killing.
All registered hunters will have to carry proof of registration during hunting and be able to show this on request.
The death warrant of fox hunting has now been signed - all that now remains is for MPs to decide what form of wording to use in the law
League Against Cruel Sports
Mr Michael said: "This bill will eliminate cruelty in hunting with dogs - it means the end of the prolonged chase and killing of wild animals just for sport.
"As the bill stands, deer and hare hunting and hare coursing are banned outright, as is using a dog below ground.
"Anyone who wants to use dogs to hunt other mammals for the specific purpose of pest control will have to prove in advance not only that it is necessary, but also that it is the least cruel means of controlling pests.
"If they can't prove this, they can't hunt - and enforcement will be simple.
"Police can check whether or not they are registered - if not, enforcement powers include fines and confiscation of dogs and equipment."
Douglas Batchelor, chief executive of the League Against Cruel Sports, said: "We warmly welcome the government's formal acceptance that fox hunting for sport is cruel and unnecessary.
"The death warrant of fox hunting has now been signed - all that now remains is for MPs to decide what form of wording to use in the law."
The bill is scheduled for a Second Reading in the House of Lords on Thursday, 17 July, just ahead of the summer recess.
Some 145 MPs, led by Labour's Tony Banks, have signed an amendment to the bill for a total ban on all hunting with hounds.
The pro-hunting Countryside Alliance says the bill would discriminate against "a responsible and law-abiding minority".
It claims the time it will take to get the measure through both Houses of Parliament could be better used "on issues that voters are actually interested in".