Britain's largest trade union Unite announced on Wednesday that it will take legal action on behalf of 1,800 employees who lost their job at Monarch Airlines.
Monarch declared bankruptcy on Monday morning after struggling to recover from the effects of terrorism and a weak pound. The airline immediately ceased activity and made more than 2,000 employees redundant.
Unite said in a statement that it will lodge employment tribunal proceedings over Monarch's alleged failure to consult staff over the redundancies.
"While, understandably, a lot of the focus is on passengers, Unite is determined to ensure that Monarch workers, who worked so hard to try and turn the airline around, are not left high and dry," said Unite national officer Oliver Richardson.
"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 by former Monarch workers," he said.
The union, which represents 1,800 Monarch engineers and cabin crew, said workers are entitled to a statutory 45 days notice under UK law, and that employees with two years or more of service should receive redundancy pay.
A consultation between the employer and a trade union representative or an elected employee representative should take place if 20 or more employees are made redundant.
KPMG, which oversees Monarch's insolvency proceedings, has said that 1,858 of the around 2,100 people employed by Monarch's airline and tour group have been made redundant.
KPMG administrator Blair Nimmo said his team would be assisting employees in submitting claims to the Redundancy Payments Office.
The Civil Aviation Authority launched an emergency repatriation scheme on Monday to fly back 110,000 Monarch customers to Britain, while cancelling the reservations of 750,000 people.
Monarch chief executive Andrew Swaffield said on Tuesday that the airline took the decision to file for administration because it faced an estimated loss of "well over" £100mn ($133mn) for the next financial year.