The future of the Lufthansa Technik plant in Rathcoole, Co Dublin, hangs in the balance today following a decision to place all 465 employees on protective notice.
The company may also lay off 150 of the workers as early as next Monday.
The move follow the workers' narrow rejection of Labour Court proposals on the introduction of new work practices.
Lufthansa Technik says it had planned a multi-million euro investment in a new engine line at the Rathcoole plant that would have ensured its future viability.
However, it says the investment was dependent on the workers accepting new work practices.
SIPTU says it believes the differences between the two sides can be bridged if management is prepared to engage honestly with trade unions.