Medical chiefs in Northern Ireland have warned that limits placed on the working hours of doctors must be honoured by the health service.
Controversial EU rules preventing doctors from working over 48 hours a week will come into effect on 1 August, the British Medical Association (BMA) said. Those hours or less are worked by around 80% of doctors.
But doctors are concerned that patients could be affected in trusts that have failed to prepare adequately for the new European Working Time Directive legislation.
Dr Brian Patterson, chairman of the BMA's Northern Ireland Council, said: "While acknowledging the huge challenge that is the change required to comply with the new European Working Time Directive, employers have had 10 years to prepare.
"We continue to have grave concerns because of the gaps in local junior doctor rotas. We will insist on real compliance by employers.
"Solutions rely on hospital managers working with doctors to ensure that doctors' time is best used and all training opportunities are maximised."