Aircraft maintenance firm SR Technics, which employs 1,200 people in Ireland, has confirmed that it has lost a major maintenance contract with Gulf Air.
The company, whose headquarters is in Zurich, was formerly known as Team Aer Lingus.
It lost three of its four contracts with Aer Lingus last year.
A company spokesman declined to say how much the contract was worth, but described Gulf Air as one of their most significant customers.
It is understood that Gulf Air has given notice that it intends to terminate the contract in June.
Part of the airframe maintenance work is done in Dublin, while other maintenance operations are carried out in the company's branches in Zurich and Bahrain.
A spokesperson said it was too early to say what effect the loss of the contract would have on SRT.
However, he stressed that no decision had been taken to change the company's current operations in Dublin or its other bases in Zurich and Bahrain.
SIPTU's civil aviation organiser Jim Finnegan said: 'As most of the Gulf Air work is carried out in locations outside Dublin, it is unclear at this stage what impact it will have on Irish operations.
'However, we are monitoring the situation and consulting with our colleagues in other unions at the company.
'We will also be seeking a meeting with management.'