"I'm really very disappointed in the manner in which this decision has been carried out and communicated to passengers," he said.
"Passengers intending to travel today or over the weekend weren’t given any warning to allow them make alternative arrangements. I do feel that Ryanair have failed in their duty of care to their customers.
"I am calling on Ryanair to publish this weekend all planned flight cancellations for the period in which this policy will be in force and to streamline their refunds procedure to ensure that discommoded customers do not have to wait for their money any longer than is absolutely necessary."
Ryanair is to cancel up to 50 flights a day for the next six weeks.
The carrier says the cancellations up to the end of October are because of a backlog in the annual leave of staff.
The airline says the backlog of annual leave must be allocated before the end of this December in order to switch to a calendar year system from January 1.
The new system will run from January to December, in a change which Ryanair says was required by the Irish Aviation Authority.
Affected customers will be contacted directly and offered alternative flights or refunds.
Ryanair says the cancelled flights accounts for 2% of its daily flights, which number more than 2,500. Between 40 and 50 flights a day will be cancelled.