The European Commission is referring Ireland to the European Court of Justice for not complying with rules on working hours for junior doctors.
The EU Working Time Directive limits doctors to a 48-hour working week.
The EC says whilst Irish law respects the requirements - in practice, hospitals are not applying the rules and there has been insufficent progress.
Junior doctors went on strike earlier this year to highlight the issue.
The EC says it considers the situation a serious infringement, which endangers both the health of the doctors and patients.