The Labour Court has heard that some staff at Ballydoyle Racing Stable worked all 28 days over a four-week period.
The standard roster for grooms and exercise riders allows them one and a half days off every fortnight.
The Workplace Relations Commission served a compliance notice to Ballydoyle on alleged excessive working hours but the stable is challenging that order at the Labour Court.
Patrick Phelan, an inspector for the WRC, told the court that the standard roster for grooms and riders at the stable did not allow the workers their right to a 24-hour rest period every week or a 48-hour period every fortnight.
He added that inspection of work records showed that in a four-week period over October to November last year showed that 19 employees worked 27 or 28 days over the four weeks.
He said there was also a concern that Ballydoyle could not show the grooms and riders were getting their daily 11-hour rest period as their daily start and finish times were not recorded.
There was a particular concern for those who had to travel to races as they sometimes arrived back to the stable late at night and then started work at 6am or 7am the next day.
Ballydoyle claims an exemption from working time regulations as an agricultural operation, but the WRC says that no longer applies to the horseracing industry.
The WRC also argues that even if it did apply, Ballydoyle would have to give compensatory rest to make up for the periods when workers did not get their statutory breaks, and that it has not shown that is doing this.
Yesterday, the Master of Ballydoyle, Aidan O'Brien, told the Labour Court that some riders have such a strong bond with their horses that they choose to come in on their days off.
