Hundreds of workers at a Huddersfield firm are set to go on strike in a row over pension changes.

Members of the Unite union voted overwhelmingly for strike action in a ballot called after a breakdown in talks with management at agri-chemical company Syngenta over controversial changes to the firm’s final salary pension scheme.

The result means hundreds of employees at the firm’s Leeds Road site will down tools and leave their desks to stage a 24-hour stoppage from noon on Thursday, May 7 – election day.

The company said it was disappointed with the decision to take industrial action after “significant” concessions were made during the 60-day consultation period following the announcement of the proposal changes last September.

The changes, which affect about two-thirds of the site’s 380 workers, see employees’ pensions based on their pensionable pay at March 1, 2015, no matter how many more years they may be employed by the company or how their pay may increase over that period.

Under the proposals, employees in the scheme could continue to make their own contributions to build up a pension, but it would not grow in line with future pay. The company’s deferred and retired members of the scheme would bot be affected.

Unite claims workers would be thousands of pounds worse off under the proposed scheme.

Syngenta said the changes were needed to tackle a pensions deficit running into hundreds of millions of pounds and ensure the scheme remained sustainable in the long term. It said the scheme would still have “clear benefits” to employees and compare favourably with many other pension schemes.

The 272 ballot papers returned showed 234 in favour of strike action and 38 against – a majority of 86% in favour. About 90% of eligible members voted.

Kevin Clarke, site convenor, said the number of votes in favour showed that “seven months on the resolve and determination of the employees to seek fairness and justice is still there”. He said members were anxious about the future and the decision to strike had been difficult to take.

Steve Donaghey, senior representative for Unite members among staff at the site said the union was talking to Syngenta, adding: “The door has always been open.”

A statement by Syngenta said: “We are disappointed colleagues have decided to support industrial action at our Huddersfield site.

“Significant concessions were made based on employee feedback during the consultation on changes impacting the defined pension scheme, which just under half of our UK employees participate in.

“These changes are essential to ensuring the long-term financial viability of the scheme, which remains a very competitive benefit for participating employees. Based on the ballot outcome Syngenta will now enter further discussions with employee and union representatives in the coming days with a view to finding a way forward.”