Monarch has been accused of breaking the law by failing to consult on redundancies ahead of its collapse on Monday morning.
The Unite trade union, that represents engineering and cabin crew has launched legal action in a bid to win millions of pounds of compensation for its members.
The union claims the firm broke the law by not giving the 1,858 staff who lost their jobs this week the statutory 45-day notice period.
Unite’s national officer, Oliver Richardson, said: “The manner in which Monarch went into administration and the way the government allowed it to happen means there is a strong claim for compensation.”
The Guardian reported a similar case brought on behalf of 1,100 former Redcar steelworkers last year ended with a £6m payout.
Monarch administrators KPMG will refund the phone bills of Monarch employees who were charged as much as £40 to hear news of their redundancy on a conference call after dialling an 0844 number.
The pilots’ union, Balpa, denounced the charge as “unbelievably cold-hearted”.