Trade union Unite has threatened legal action against Grangemouth chemicals plant owner Ineos after the firm said it intends to end collective bargaining agreements.

Unite’s senior Scottish official Pat Rafferty said the announcement in April would prevent the union from representing workers at the industrial complex.

Mr Rafferty said last night he will lodge an appeal to block the move with the Central Arbitration Committee (CAC), the government body which oversees the regulation of industrial relations.

Mr Rafferty said: “We intend to protect our legal right to ensure our members are represented by their union. My sincere hope is that Ineos rescind the notice to derecognise Unite and avoid an unnecessary legal action.”

In a letter to staff last month, Ineos said: “We will defend your right to be represented by a union, although other options such as through a works council can be envisaged, but not by Unite.”

Unite currently represents a majority of staff at the plant which employs around 1,300 workers at the refinery and a further 400 people in the petrochemical and infrastructure divisions.

The fresh dispute comes three-and-a-half years after industrial action led to a threat by Ineos to close the plant for good.

The news was broken to the workforce in October 2013. Ineos said a decision on whether to restart the refinery would be taken once the "threat of strike action" had been removed.

The company later reversed its decision after workers agreed to a survival plan which included a three-year pay freeze.

Speaking in April, Unite’s assistant general secretary Howard Beckett described the move to end collective bargaining agreements at Grangemouth as “an incredibly foolish attempt to undermine the democratic rights of workers”.

He added: “After three years without a pay rise there is bound to be difficult negotiations, but Unite's demand for a 3.25% rise is more than reasonable and our intention remains to achieve a negotiated agreement.”

Ineos has not yet responded to a request for comment.