A strike by contract labourers demanding a “longstanding” increase in their wages has stalled loading of coal onto ships at Haldia port since July 1.

While leaders of a Trinamul Congress-backed trade union are insisting that the strike is wage-based, port sources claimed the impasse was created deliberately by the ruling party to thwart the loading by Prabha Utility Services, a firm based in Gujarat’s Vadodara.

It had won the contract for the loading over Sibdurga Visvakarma Engineering, a Haldia-based firm reportedly close to local Trinamul leaders. Sibdurga had won the contract in the two previous years.

The sources said 20 labourers, who handled a conveyor belt that loaded coal onto ships, had announced the strike during the changeover to the new contractor on July 1.

“Trinamul is behind the strike to prevent the Gujarati firm from starting the work here. It is well known that Sibdurga was a concern patronised by Trinamul leaders in the area,” said Pradip Bijoli, a leader of the RSS-affiliated Bharatiya Mazdoor Sangh.

Sources in Prabha Utility Services said the workers had demanded a 35 per cent hike in the wages during their meeting with the firm’s engineers on June 31. “That was too much. We knew that we had to absorb workers. But when we were awarded the contract on June 26, nobody told us about a wage hike,” said a source.

“Our demand of a 35 per cent increase is not new. We had raised the demand with Sibdurga as well. It makes no sense for us to agree to work for a new contractor at the same rate,” said one of the striking workers.

The port sources said the main fallout of the strike was the delay of weekly shipments of 35,000 tonnes of coal to a Tamil Nadu government-owned thermal power plant in the southern state.

“The shipment normally takes 10 days to reach Tamil Nadu. If the problem here is solved, they might shift their business to another port. We are currently their biggest supplier,” said an administrator at the port, who added that the seemingly minor role of a single conveyor belt was potentially costing the port lakhs of rupees a day.

S. Chakraborty, the deputy manager of the port, declined comments. The port’s general manager Amal Datta said he was in Chennai and would look into the matter soon.

“Our union is not stalling anything. The contractor will have to abide by the rules,” said Sibram Sarkar, a leader of the Trinamul-backed trade union.

Officials of Prabha Utility Services said they had sent a letter to the assistant labour commissioner of Bengal on Wednesday, seeking a swift and sensible resolution to the strike.