Irish Ferries is attempting to cut its costs

The company is blaming the action on a failure to negotiate an agreement with two trade unions over cuts in jobs and increases in working hours.

Routes between Holyhead to Dublin and Pembroke Dock to Rosslare are being hit with 600 workers are affected by the action.

The Ulysses super ferry between Holyhead and Dublin will continue to run.

Ferries affected Jonathan Swift, between Dublin and Holyhead Isle of Inishmore, between Rosslare and Pembroke Dock Normandy, between Rosslare and Roscoff

In a statement released on Tuesday, Irish Ferries said it regretted the action adding: "In deciding upon the specific action taken, Irish Ferries has been extremely conscious to ensure that the minimum degree of inconvenience and disruption would be caused to passengers and freight customers.

"[This is] consistent with the necessity to move forward and introduce cost-cutting measures as set down in various communications to representatives of the ships' officers and crew members involved."

A spokesman for the company stressed the withdrawal of services was only meant to be temporary but did not know how long it would last.

Last Tuesday, around 600 company workers received letters saying that, unless negotiations could be advanced by 20 February, the services would be suspended.

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Spokeswoman Emma Hargreaves said at the time that any suspension would not begin before 27 February.

However, the Seamen's Union of Ireland warned that if the other three services were suspended, its members would not continue to operate the Ulysses.

The union has said the dispute is mainly about leave.

At present Irish Ferries staff get six weeks annual leave, but a union spokesman says the company wants to reduce it to four weeks, which is what rival ferry company Stena Line staff receive.

Members of Siptu, which mainly represents higher ranking officers, are also contesting the changes.

Irish Ferries has recently set itself the task of shedding 52 sea-going staff and saving �2.3m a year, after an investigation found it had "the highest crew ratio in the British Isles".

But it has not been able to agree with the unions, despite negotiations at the Irish Labour Court and Labour Relations Commission.