The Irish Hotels Federation is challenging the way wages in the hotel sector are set by the Labour Court.
The case is being taken by Clare hotelier Michael Vaughan and the IHF, who argue that the way wages are fixed by Joint Labour Committees and the Labour Court contravenes employers' rights.
Unions say that if the hoteliers win their case, it could reduce employment protection for up to a 250,000 low paid workers in other sectors.
Almost 125,000 people work in the hotel sector. Outside Dublin and Cork, their wages and conditions are set by a Joint Labour Committee and the Labour Court.
The latest wage increase was due on 16 November, but Mr Vaughan and the IHF obtained an injunction preventing the Labour Court from finalising the JLC proposals.
The employers argue that the JLC mechanism of fixing wages breaches their constitutional rights.
Unions say that many vulnerable workers in this labour intensive industry would have inadequate protection without the JLC system.
The Commercial Court hearing is expected to last four days. Industrial relations observers are watching this case very closely.
If the employers win, up to a quarter of a million workers in sectors including hairdressing and contract cleaning could lose some of the protection they currently enjoy.
A victory would also erode the powers of the Labour Court - the scope of which has already been significantly diminished by last year's Ryanair ruling.
