The company proposed a pay cut of up to 20% just after Christmas. According to Unite, the proposed cuts are illegal because a company cannot enforce pay cuts on employees unless it is negotiating with a recognised trade union.

National officer Steve Sibbald said: "Our lawyers have written to them and said that, if they choose to impose these cuts, there will be a legal challenge that could be very expensive.

"We will be looking for a protective award, which could be up to 90 days' pay for each employee.

"We have never been derecognised there, so if they want to follow this route they should be talking to us about it."

Meanwhile, Unite has also questioned the timing of paycuts, which follow a substantial increase in BGP directors' pay in 2011.

In its results to 31 May 2011 it is revealed that BGP's highest paid director received an increase of 33.7%, from £163,000 to £218,000, while total directors' remuneration increased from £414,000 to £504,000 (21.7%).

Sibbald added: "We will be asking them how they can justify that and expect employees to take a 20% pay cut. Obviously they weren't in that much trouble last year if they could afford to do that."

However, GBP Group chairman David Holland refuted the claims. He said: "Directors took a 20% pay cut last year. One director was terminated and his salary frozen until the end of the year, but which was paid out at the time. So while an increase is shown, a 20% cut was actually taken by all directors."