The union said that the 37 employees, who picketed the company’s Sunderland-based headquarters, had been left with "no choice" following the dispute which began after Paragon launched a 90-day consultation on employee contracts.

Unite regional officer Dave Telford said that Paragon is proposing to dismiss employees and re-employ them under "unfair" terms, which include changes to shift premiums and overnight working allowances.

The 24-hour walkout began at 7am yesterday morning and will be followed by another 24-hour stoppage from the beginning of the late shift at 7pm on Friday.

Further strikes are planned for the same days next week.

A spokesperson for Paragon UK said: "We can confirm that following a 90-day consultation period regarding the terms and conditions of current contracts, the union members based at our Sunderland manufacturing facility have chosen to take industrial action.

"We are still in discussion and have no further comment to make on the matter at this stage. While negotiations are on-going, our commitment is to meeting with the requirements of our customers to ensure that we continue to deliver the level of service they have come to know and expect from the business."

Paragon UK is a multi-site business with a turnover of more than £45m.

Last month Unite members at packaging specialist API Foils Europe went on strike, also over proposed changes to contractual terms and conditions.