HMRC IR35 rules are changing next April making contractors liable for determining the tax status of off-payroll professionals.
And Balfour Beatty is understood to be one of the first major contractors to audit freelancers employed via a personal service company.
One white collar worker said: “I’m freelance at Hinkley Point for Balfour but all of us have been told we might have to transfer to PAYE under the new rules.
“Some people are talking about working for other contractors because Balfour is the first to really act on this.”
Current rules allow workers to be employed via a personal service company (PSC) which determines whether IR35 tax rules should apply.
That responsibility will shift from April to contractors who will determine employment status.
Balfour said it was looking at the situation across its whole business to see how the tax changes would impact employment models.
A spokeswoman said: “We want to act now and get