More than 200 hospital staff in Sheffield have been told they must retire.
Sheffield Teaching Hospitals NHS Foundation Trust wrote to 203 staff aged over 65 informing them their contracts would cease on 1 October.
The letters were sent on 31 March, a week before the default retirement age of 65 was banned.
The hospital said it was following its policy that if a post was no longer required the employee would be retired.
'Shabbily cast aside'
Margaret Sharpe, 67, who received a letter, said she had worked for the trust since 1976.
"My age and capability have never been questioned, so why suddenly now?
"You just feel that you're being shabbily cast aside, when you know that you have got work within you.
"The day when I know I can't work I would feel it in my heart and that would be the time to go."
In a statement the Trust said it did "acknowledge the service that people give to the hospital".
"However our retirement policy, prior to the recent change in legislation, was that when a person reaches 65, if their post was no longer required to meet service needs at that time or in the future they would be required to retire."
The Trust is currently trying to save £40m this financial year.
Andy Freeman from the union Unison said: "I think the Trust's been very clumsy in the way they've handled this because retirement is a very individual decision.
"Some of these people are continuing to work because they have to.
"I think this is a cheap way of getting people out of the door, because obviously it's an alternative to redundancy."
Employment lawyer Diamuid Deeney said: "Not only are people living longer, healthier lives, but people also approach retirement and they realise they can't afford to retire.
"If anyone is worried about [being told to retire] that then please take proper advice, because in the law there are no sweeping generalisations there may be different situations for each different worker."
He added that under new regulations people could continue to work beyond the age of 65, but would be subject to performance management and if not capable of doing the job could be dismissed.