SIPTU general president Mr Des Geraghty said that a failure to pay the next phase of benchmarking payments would constitute a breach of the national pay agreement.
Responding to a call by Fine Gael leader Mr Enda Kenny for the shelving of the benchmarking process, he told ireland.comthat reneging on the deal would also be "very wrong".
"It's a fundamental part of the national agreement. I would be satisfied that if benchmarking is applied correctly it will be a good deal for the State in the long run," he said.
However, the employers' representative body IBEC was more supportive of Mr Kenny's comments.
Mr Turlough O'Sullivan, IBEC's director general, said he had called for the benchmarking agreement to be renegotiated as far back as last July.
While not specifically endorsing the Fine Gael leader's comments that it should not be paid, Mr O'Sullivan said it should not be paid "in its current form" and that the deal should be "renegotiated".