Tony Burke, assistant general secretary at the union, said that a number of companies are approaching the members with "flimsy arguments" for pay cuts and working practice changes and threats of redundancy if terms are not accepted.

"There is no way an employer can provide a cast-iron guarantee that no redundancies will be made and the National Agreement provides flexibility without the need to cut pay," he said.

The union has urged members to reject any temporary reductions in pay or changes to contractual rate of pay.

Unite said that it would support a ballot for industrial action in instances where members are prepared to resist cuts in pay or changes to the National Agreement.

Burke said that strikes were inevitable, but added that the union was not close to balloting members at any company at present.

He said: "A company must be prepared to open the books to members. We are hearing reports of members being pressed to take pay cuts when they are working overtime. This is unacceptable."

The warning came as Wyndeham became the latest company to enter into a 30-day consultation, which came at its West Sussex-based sheetfed site Wyndeham Grange, which is expected to result in redundancies and a potential pay cut.

According to Unite, staff were informed on 20 May that Wyndeham planned to cut around 32 positions at the 96-staff site, as well as implementing a 10% pay cut for the remaining staff.

Unite national officer Steve Sibbald said: "It is another company taking advantage of the economic situation. They don't really need the cuts.

"People haven't got anywhere else to go, but I imagine in a few years, when there are other options, people will leave in their droves."

However, Wyndeham chief executive Paul Utting said that the consultation was necessitated by the falling demand from both the commercial and public sector.