American Airlines Group has filed a suit against two unions representing its mechanics seeking a directive from the court to block an ‘illegal’ slowdown that could disrupt US summer travel.

In the lawsuit filed in the Northern District of Texas federal court, American Airlines Group accused the mechanics unions of directing a slowdown to disrupt operations to improve their position in labour talks, which commenced in 2015.

The world’s largest airline in terms of passenger traffic, American Airlines said that the mechanics’ action had intensified recently after causing 650 flight cancellations and more than 1,500 maintenance delays since February.

In the lawsuit, the airline said: “American estimates that, for each day that the slowdown continues into the summer, it will disrupt the travel plans of approximately 3,400 additional passengers per day.”

In April, American Airlines had reduced its 2019 profit forecast, estimating a $350m hit from the worldwide grounding of Boeing 737 MAX planes in March, forcing thousands of separate flight cancellations during the busiest travel season.

According to analysts, a prolonged MAX grounding and mechanic-related disruption could further affect the airline’s profits.

American Airlines said that it is also holding discussions with unions representing its flight attendants and pilots, whose contracts become amendable in 2019 and 2020, respectively.

The airline said that it has offered a proposal that includes pay and benefits to its mechanics unions, namely Transport Workers Union of America and the International Association of Machinists.

The unions alleged that American Airlines is trying to outsource more maintenance jobs, a move the airline said is necessary to cover increased wages.

“For each day that the slowdown continues into the summer, it will disrupt the travel plans of approximately 3,400 additional passengers per day.”

Last year, American Airlines had asked the National Mediation Board to help negotiate an agreement with the unions but said that the discussions were stopped after the last session on 25 April.

It said that since then, union action had caused 14 flight cancellations a day compared with an average of eight daily union-related cancellations previously.

Southwest Airlines had recently reached an agreement in principle with its mechanics union after the US Federal Aviation Administration warned that a prolonged contract dispute could pose safety concerns.