A majority of the workers at Kerry's biggest manufacturing plant, Liebherr Container Cranes in Killarney, staged a 24-hour stoppage yesterday to highlight concerns over a pension scheme.
The company, which is currently very busy dealing with orders, expressed astonishment at the strike action.
A spokesman for the Siptu workers at the Killarney factory said the workers had rejected a Labour Court recommendation and balloted for a strike.
Yesterday was the first of a series of planned stoppages at the 49-year-old German-owned factory which employs up to 500 people. There is also a complete ban on overtime.
The issue relates to a decision by Liebherr Ireland in 2004 to close a defined benefit pensions scheme for new employees and to introduce a defined contributions scheme "of lesser value and on less favourable terms", Donal Tobin, Siptu's branch secretary, said.
Workers wanted the defined benefit scheme reopened for all.
Mr Tobin said that pensions were a major issue for his union. There was a deliberate attempt by employers to downgrade pension schemes, he claimed.
However, he denied that Liebherr, a company that was going well, had been targeted to highlight Siptu's general pensions campaign. "This is an issue for the Liebherr site only," Mr Tobin said, adding that talks had been going on since 2004.
The company has responded strongly to the overtime ban and the threat of further stoppages. It remains opposed to reopening the defined benefits scheme but says it is willing to engage in talks.
In letters to the union and workers released by the company to the media, Liebherr said it was "greatly disappointed" at the rejection of the Labour Court's recommendations and a decision to proceed to industrial action without availing of talks chaired by an officer of the Labour Relations Commission.
Gross wages for hourly-paid employees last year averaged €48,500 and "over 100 hourly-paid employees earned well in excess of that", personnel manager Tom Foley said.
Skilled production personnel earned up to €44,000 for a 36.5-hour week under national pay agreements and terms agreed last October by the company. This was apart from overtime and service benefits.
Industrial action had "enormous potential" to destroy trust built up over the years with Liebherr customers. The crane and container factory currently had an "unprecedented order book" and the union's action could cause "irreparable damage to our image and reputation", Mr Foley warned the union.
"The result of this ballot is even more inexplicable if considered in the context of the current crisis affecting manufacturing industry in Ireland."
The ban on overtime in particular and the threat of a series of stoppages in pursuit of unrealistic claims would prompt "an urgent rethink" of current employment levels and would particularly affect 91 temporary employees, Mr Foley said.
Any excess capacity requirements could readily be deployed to sister companies overseas, he added.