The government wants to ban cigarettes from being openly on sale
Newsagents are threatening to boycott the Labour Party at the next general election if legislation bans them from openly displaying cigarettes.
They say the move - due to be debated by MPs on Monday - would drive hundreds of small retailers out of business.
The National Federation of Retail Newsagents (NFRN) say it will be "very bad news for Gordon Brown" if the vote goes against newsagents.
Retailers say it will cost more than £250 million to implement the ban.
This, they claim, will be because shops will have to be refitted after removing the displays.
A spokesman for the NFRN told the BBC's Politics Show: "No-one wants to see youngsters smoking, but there is absolutely no evidence from the three other countries in the world that have introduced a display ban that it stops underage smoking.
"If the vote on Monday goes against newsagents - our 18,000 members - then they will vote with their feet. This will be very bad news for Gordon Brown."
The move is part of the government's Health Bill, given its second reading in the Commons in June.
Ministers and health campaigners say putting cigarettes on open view encourages young people to buy them.