A partial smoking ban will widen the health gap between the poorest and richest in society, warn UK doctors.
The consultation on a smoking ban will end next month
They say current proposals for a ban in England in 2008 would mean those in poorer areas would struggle to find a smoke-free pub.
The government is proposing exemptions for pubs that do not serve prepared food and private membership clubs.
The British Medical Journal study looked at the catering status of pubs in Telford and Wrekin in Shropshire.
Dr Alan Woodall and his team at the Telford and Wrekin Primary Care Trust then mapped these by postcode to calculate a deprivation score.
There were 174 pubs in the borough - 99 (57%) serving catered food, meaning that under the proposals 75 (43%) would be exempt from the ban.
When all licensed members' clubs were included, 127 (56%) would be exempt.
The government's White Paper "Choosing Health" estimates 70-90% of pubs in England would have to impose a smoking ban.
But based on the Telford and Wrekin figures, the study's authors estimate that two thirds of pubs in deprived areas would be exempt, compared with only a quarter in affluent areas.
When private members' clubs were included, two-fifths of establishments in affluent areas and four-fifths in deprived areas would be exempt.
The researchers said: "Although this is a small study, our results suggest that people in deprived areas are more likely to live near pubs exempt from legislation to protect them against smoking.
"This is likely to worsen inequalities in health and smoking prevalence."
They called for a ban on smoking in all enclosed public places.
Anti-smoking groups, such as Action on Smoking and Health (Ash), back a total ban, as does the British Medical Association.
The BMA's Dr Peter Maguire said: "The only way forward is for the government to follow the leadership shown by politicians in Scotland, Ireland and Norway and impose a complete ban on smoking in all public places in England and Wales.
"The BMA urges the government not to delay in implementing this legislation."
But a spokeswoman from the Department of Health said the proposal for a partial ban was based on many factors, including public opinion.
"The public were far less supportive of measures to make all bars and pubs smoke-free.
"We are currently consulting on the proposals in the White Paper before legislation goes to Parliament, and we will look carefully at all the evidence put forward."
The consultation will close on 5 September.
Simon Clark, director of the smokers' lobby group Forest, said: "People are perfectly capable of deciding for themselves whether or not they want to go into a pub that allows smoking.
"On a voluntary basis, there are an increasing number of smoke-free pubs, but this should be left to market forces. If more people want smoke-free pubs they will vote with their feet."
Ian Willmore from Ash said: "Exemption will make inequalities worse not better.
"We are optimistic that the government will look at the evidence it is getting during the consultation process and may decide to go ahead with comprehensive legislation without the exemption."