The oncology clinic at Letterkenny University Hospital has been cancelled for two weeks in a row.
It's understood that nursing shortages may be the root of the problem.
Donegal Deputy Pearse Doherty has contacted management at the hospital, requesting urgent clarification.
Deputy Doherty, who has been contacted by those affected, says both patients and their families are worried of the effects that this will have on their treatment.
He has described the situation as outrageous: