Easter Mass was celebrated in Letterkenny University Hospital "contrary to current Government guidelines and without authorisation," the Saolta Hospital Group has confirmed.
It is understood a number of people were present at the mass, which was celebrated in the hospital chapel.
In a statement regretting that there was non-compliance with Government guidelines, Saolta stated that "the hospital can confirm that no further religious services will take place in the chapel while the country is at Level 5."
The statement added that "the chapel will remain open for private prayer only until the guidelines advise on the recommencement of religious services".
Under current Level 5 restrictions, religious services are only permitted to be held online, although places of worship remain open for private prayer.
The Government has said this will be by 4 May.
Religious leaders have called on the Government to allow people to return to religious services as soon as possible.
Last month the Catholic Archbishop of Dublin said he will continue to emphasise to the Government the importance of the earliest possible return to worship.
Dermot Farrell said there would be "further direct engagement with Government" to ensure that specific positive consideration is given to public worship by the end of April.
The Archbishops met the Taoiseach in February to ask him to consider public worship at Easter and to increase the maximum attendance at funerals from 10 to 25.
The number of people allowed attend a funeral will increase to 25 from Monday 26 April.