Employees must leave their trades union or risk losing their jobs, a car transport firm has warned.
Car logistics company Autologic wrote to all 280 drivers demanding they give up their membership of Unite, the country's biggest trade union, and threatening them with redundancy if they refused to do so.
In the leaked letter Autologic accused the union's shop stewards of "looking after themselves handsomely". It also claimed the union of threatening behaviour and said Unite rewarded workers who do not work hard.
"Autologic can offer you good pay, good conditions and a good future. The trade union can offer you tea and biscuits when you've lost your job," the letter said. "We will not be able to offer job security and good futures unless the trade union stranglehold on this company is removed," it added.
A company spokesman said: "It has been disappointing that the engagement process with trade union representatives, so far, has been unconstructive."
Unite has not ruled out legal and industrial action against the firm. A spokesman said: "I have never seen a letter like this in my 25 years in the industry. Unite will take all legal and industrial action to protect its members."
During the dispute, Autologic's managing director, Avril Palmer-Baunack, bought a new Porsche Cayenne. Its tyres have since been slashed.