Hundreds of supporters of fox hunting from Wales joined protests outside the Commons as MPs debate a ban.
Supporters of hunting will hold a rally at Westminster
Wednesday's vote on the Hunting Bill could herald a complete ban on hunting with dogs in Wales and England.
The debate in the Commons will be followed by a free vote in which MPs will decide whether to support a ban.
MPs are likely to support restrictions and the government has said that any opposition to the bill in the Lords will be overridden.
Ministers have said that if the bill is made law in 2005, a ban on hunting would not be enforced for a two-year period.
But supporters of fox hunting in Wales have claimed that even with a two-year delay, a ban would have a "catastrophic" impact on the livelihoods of many involved in hunting and have vowed to oppose it.
Coach-loads of hunt supporters from across Wales are at a rally at Westminster.
Mair Hughes, a member of the Llangeinor Hunt, in south Wales, said around 100 people from the hunt would be in London to protest.
She added: "My husband is a farrier and my son is an apprentice in the same trade.
'Ignored by MPs'
"The foot and mouth restrictions hit us very hard a few years ago when there were restrictions in the countryside.
"Around 75%-80% of our business comes from hunting, so a ban would be catastrophic."
Mrs Hughes added: "We are frustrated, because we believe we have won the argument over things like the need for pest control, but there is not a lot we can do - all that is being ignored by the back-bench MPs."
But opponents of hunting with dogs said a ban would open up new economic opportunities for many in the Welsh countryside.
Richard Tiller, a representative of the League Against Cruel Sports in west Wales, told the BBC Wales news website: "I think that with fox hunting banned, the countryside will be a happier, friendlier, more welcoming place.
"There will be economic opportunities for people in things which have a wider appeal like drag hunting and equestrian sports
"Opponents of hunting have held a large majority for a long time, but have been frustrated.
"A vote to ban hunting is a vote for democracy.
"The League Against Cruel Sports is marking its 80th year soon - I hope we don't reach 100."
Rural affairs minister Alun Michael has said any planned postponement was to give people involved in hunting "adequate time" to re-home dogs and "refocus" business.
"This period will give those involved in hunting more than adequate time to cease the activities which are to be banned," he said last week.
Hunting with hounds: the end is nigh?
This could involve "the dispersal or re-homing of dogs", the refocusing of any business activities on alternatives like drag-hunting.
Lembit Opik is the Liberal Democrat MP for Montgomeryshire and co-chair of the Middle Way Group on hunting.
He said that Wednesday was "not looking good".
"The Government has given the pro-ban lobby the opportunity to go on in there, not listen to the arguments and pass a ban," he said.
"The majority of the public actually oppose the criminalisation of hunting with dogs, that's not something you hear very often from the RSPCA or the League Against Cruel Sports.
"Banning hunting with dogs will actually increase suffering in the countryside not reduce it.
"Shooting and poisoning will inflict greater suffering. If there is a ban today the fox will suffer," he added.