The move underlines their determination to revamp industrial relations in the M&E sector despite opposition from rank-and-file electricians.

The majors plan to quit the JIB agreement next March and have written to 6,000 workers explaining the reasons behind their decision.

Now five – Balfour Beatty, Crown House Technologies, Spie Matthew Hall, Shepherd Engineering Services and NG Bailey – have told the union Unite that workers must sign new deals by December 7 or face the sack.

The latest move has angered Unite officials who want to see the JIB maintained and fear any new deal will lower pay and skill levels – a charge fiercely denied by the employers.

Bernard McAulay, Unite national officer for construction said: “These rogue employers should pull back from the brink as their attack on workers’ skills, pay and terms and conditions is causing widespread anger among workers.”

The union now wants to sit down with the breakaway eight which also includes Gratte Brothers, MJN Colston and T Clarke.

Unite claims a split is developing between those taking a hard line and the rest of the rebels.