One in five working men's clubs thinks it will end up closing once a smoking ban comes into force in England and Wales, a BBC survey suggests.
Smoking will be banned in pubs, clubs and enclosed public spaces
Of the 560 clubs which responded, four out of five thought they would lose money as a result of the ban, while only 1% anticipated a rise in takings.
The ban will start in Wales on 2 April and in England on 1 July.
Smoking will be banned in pubs, clubs and enclosed public spaces, even if the area is open only to private members.
Originally the government had been in favour of allowing smoking to continue in private clubs, but the House of Commons threw out the idea.
Kevin Smyth, the general secretary of the Club and Institute Union, said the ban could force some clubs to close.
He told BBC Radio 4 's Today programme: "Gaming permits, extra increases in licensing fees and now another set of legislation which looks as if it will almost certainly reduce the number of members coming into clubs is a great concern.
"I can understand why a number of clubs feel this may be the straw which breaks the camel's back."
Smoking was banned in enclosed public places in Scotland in March 2006 and was hailed as a success by First Minister Jack McConnell on the first anniversary on Monday.
"Even after one year, Scotland is a healthier place and people, both in work and at leisure, are able to avoid the atmosphere which in the past caused them health problems," he said.
But the BBC News poll of working men's clubs in England and Wales found that one in five thought the smoking ban would cause them to close down.
A quarter of the clubs which took part said they thought the rules would be difficult or near-impossible to enforce.
"We do not know how we are supposed to 'police' this ban when we cater for private parties. People will probably get drunk and light up anyway," said Mark Proctor, secretary of a club in Burnley.
Many representatives of the clubs said they felt it was wrong to include private bars in the ban.
PM Rawlings, the treasurer of a club in Basingstoke, said: "I feel that the government should have honoured their election manifesto to exempt private members' clubs, as for all other purposes we are not a public place."
Summary of the clubs' responses:
- 20% thought their clubs were likely to close as a result of the smoking ban
- 83% thought they would lose money
- 1% thought their takings would rise
- A quarter thought the ban would be difficult or near-impossible to enforce
- 40% were confused about the public spaces covered by the ban