Electrical union AEEU is demanding an investigation into Beaver Management Services, which supplies more than 100 electricians and labourers to the project, after learning that its operatives are working on a self-employed basis.
Electricians working for M&E firm Balfour Kilpatrick are demanding a wage rise of up to £120 a week to match the rates paid to BMS electricians. They claim the firm is operating a bogus self-employment scheme in an attempt to avoid paying National Insurance.
A Balfour Kilpatrick electrician said: "If they remain on the site, we want parity of pay or there'll be trouble." Electricians were due to hold a meeting on Thursday and said they were not ruling out a work stoppage.
Building has obtained a copy of a BMS contract that states that a general labourer is a subcontractor and, as such, is not entitled to holiday or sick pay.
BMS also insists that operatives carry public liability insurance, which is required by all subcontractors, and deducts £12 a week plus VAT to pay for the insurance cover and other "invoice administration".
Electricians say BMS operatives clock in and out with directly employed workers and are supervised by BMS foremen. According to Inland Revenue guidance, this means an operative is an employee.
BMS managing director Bernard Goodchild said the firm's operatives were genuinely self-employed. He said: "They don't have to clock in at the opera house, and most of them only work half a week at the project." He added: "They're not taking orders but, ultimately, there has to be someone at the top of the chain. We have supervisors on the project, but they are providing services on a skilled basis and take orders from the main client." He said all BMS operatives would pass the Inland Revenue's £30 000-turnover test for self-employed status and said the £12 deduction for insurance and administration was necessary because many BMS operatives did not employ accountants.
A spokesperson for Balfour Kilpatrick said: "We insist that agencies and subcontractors used by us comply with the law. We have assurances from Beaver that they comply."