Patients may be being put at risk because hospital bosses are closing rest rooms, junior doctors say.
Junior doctors use the rooms to get some sleep during shifts
The on-call rooms, which contain a bed and shower, are used by junior doctors during quiet times on night shifts.
But the British Medical Association said scores of rooms had been closed in hospitals as part of cut-backs after new working time restrictions started.
The BMA said it is depriving doctors of valuable rest and risking patient care, the BMA News magazine reported.
Dr Andrew Rowland, joint deputy chairman of the BMA's junior doctors committee, said a number of on-call rooms had been closed since the EU working time directive kicked in for junior doctors last year.
The rooms were used by doctors while they were on call - sometimes for 32 hours at a time - to get rest when they were not needed.
During the night, junior doctors are only called to deal with emergencies in A&E and if inpatients become ill.
Since the change in the law last year, the 42,000 UK junior doctors are limited to 58 hours a week - due to be reduced to 48 by 2009.
The change has prompted many hospitals to introduce shifts, often for 12 or 13 hours, to cover night care.
Dr Rowland said: "While the hours have been cut, 13 hours is still a long time. Doctors still benefit from a little rest and sleep.
"But with the rooms being closed, this is being denied to many doctors. This in turn may risk patient care.
"Junior doctors can be called on if a patient develops chest pain or breathing problems, it is important we are rested."
He said the rooms, which are traditionally linked to wards, have been turned into offices or just left empty.
"I don't understand it. They cannot cost a great deal to keep open, yet can make such a difference. I would urge hospitals not to close them."
He said it was not clear how many had been shut, but it was a pattern that was emerging all over the UK.
The Department for Health said it was up to individual NHS trusts as to how they implemented the working time directive.
But the spokeswoman added patient care "should not be compromised".