Siptu is considering further action at the Conoco Phillips oil storage facility in Bantry in a dispute over pay parity.
Workers at the oil terminal ended a 48-hour work stoppage this morning in the protest at the lack of pay parity with colleagues working at the National Oil Refinery Authority in Whitegate.
Siptu branch organizer Eddie Mullins said the union would review its options, but warned that if the company did not respond more positively, it would have to consider full industrial action at the plant.
Mr Mullins said the union was disappointed but not surprised at the company's failure to resume negotiations.
"Our members conceded jobs and gave up opportunities for significant overtime earnings in return for management commitments in 2004 that time off in lieu for unsocial hours working would be interpreted generously", he said.
"We remain available for talks but, in their absence, will be planning further action, " Mr Mullins added.
Mr Mullins said that the 2004 agreement operated well for the first two years, but has since been reinterpreted by a new management team "so that the current situation represents a very real deterioration in the quality of employment, as well as in pay terms."
He said that while the company could argue that it was "within the letter of the 2004 agreement", it was not abiding by its spirit.