Licensees could be forced to implement the 48-hour working week if the European Commission (EC) gets its way.
The Commission is expected to slam Britain's opt-out of the working time directive in a report due out next month.
Britain is the only member state that allows workers to opt out of the European legislation - which limits working hours to 48 a week.
The EC is expected to claim British employers are abusing the opt-out clause.
This could be disastrous for pub managers, many of whom voluntarily work more than 48 hours. According to The Publican Market Report 2003 the average weekly hours of a licensee is 75.
Although self-employed licensees will not have to meet the requirements, pub managers and other staff will.
If the clause is dropped by the UK following pressure from Europe, licensees and pub companies may have to employ extra staff to cover long hours. Barstaff paid an hourly rate could suffer financially, while salaried managers could be forced to job share.
Tony Payne, of the Federation of Licensed Victuallers' Associations, said: "Europe is not taking into consideration that a lot of people on low pay want to work extra hours.
"Self-employed licensees put in a lot of extra time and this directive could put pressure on many managed estates. It could also affect tourism during seasonal periods. I hope the government takes a sensible attitude."
But Trades Union Congress general secretary Brendan Barber said: "The UK is the only EU country that allows everyone at work to sign away their working time rights. There is wide evidence that there is no free choice for the majority of long hours workers."
Europe shelves same rights plan
It is understood that Europe's plans to give part-time and agency staff the same pay and conditions as permanent staff has stalled permanently. The EC wanted workers who were employed for six weeks or more to receive the same rights as permanent staff. But Britain and other opposing countries wanted employees to receive the same rights when they have been in their job for a year.
The trade had feared that the regulation would make it more expensive to employ temps for holiday and seasonal cover. A poll on thepublican.com at the end of 2002 found that almost three-quarters of licensees would be put off employing temporary staff if the ruling was passed.