Air India said it was closely monitoring the situation.

Troubles are growing for Air India Ltd, with aircraft technicians planning a strike later this month after the company’s pilots last week expressed concerns about being overworked and underpaid.

Technicians at AI Engineering Services Ltd. will go on strike on April 23 due to various issues affecting their “well-being” and “career development”, All India Aircraft said. the Maintenance Engineering Alliance wrote in an April 8 letter to the CEO.

An Air India representative said it was closely monitoring the situation.

Unrest among aviation workers could hamper India’s air travel boom. Pilots and aircraft engineers are crucial to supporting the country’s rapid fleet expansion, with IndiGo, Air India and Akasa ordering more than 1,100 aircraft between them.

The strike will further disrupt the Indian aviation industry. Hundreds of flights were canceled last week after some pilots at Vistara Airways, jointly owned by Air India parent Tata Group and Singapore Airlines Ltd., called in sick en masse due to fatigue and pay cuts. The airline is cutting 25 to 30 flights a day to create a buffer in its roster to prevent more cancellations.

AI Engineering’s largest client is Air India.

The letter said employees at the company were upset about the lack of career advancement opportunities because they had not been promoted in the past seven years. The management promised to revamp the pay structure for technical staff who have been with the company for at least two years but it has not yet materialized. The letter said contract workers, who make up 75% of the company’s workforce, felt discriminated against because they had to accept longer notice periods and did not receive as many benefits as permanent employees.

A representative from AI Engineering said management has begun discussions with the union to resolve the issue. AI Engineering has revised the salaries of all employees except technical staff as the court case is pending, the company said. The company plans to revise wages for technicians after a union withdrew a lawsuit demanding equal pay for contract and permanent workers.

Meanwhile, Air India pilots have echoed the concerns of Vistara employees, saying issues of underpayment and overwork are “systemic” problems in the Tata aviation empire.

The letter said aircraft technicians had urged management to resolve the issue to avoid potential disruption caused by the strike.