Manchester Airport has allegedly sacked security staff and not given them fair rights to a grievance hearing, according to the Transport and General Workers' Union.
The union claims the workers, mostly women, were sacked after failing to reach agreement on new contracts.
Manchester Airport says 16 employees have been given a few days to think about their future after being offered new contracts.
The dispute over new contracts led to a series of strikes earlier this year at the airport.
T&G regional industrial organiser Brian Bowen said: "This really is a case of Alice in Wonderland justice of 'sentence first, verdict afterwards.'
"The majority of these staff could not do the hours which the airport told them they had to work under the new arrangements because they had childcare and other responsibilities.
"They were first turned away from work and then on Wednesday they were given just eight hours notice of a grievance hearing. That is no way to carry on, so we made an agreement with Manchester Airport that, to allow the grievances hearings to be done properly on all sides, they should be rescheduled for 13 June.
"Now, with a cynical twist and a callous sense of timing, they are told they have been sacked before their case can be properly heard."
More than 570 security staff have accepted new contracts or other packages and bosses have spent weeks trying to persuade the 16 to stay with the company, the airport said.