Unions have been lobbying the government over the Posted Workers Directive, which says that British firms employing temporary workers must pay them the same rate as UK workers.
Confederation industrial relations director Jerry Lean warned that the industry could face industrial action over the issue. He said: "We could face a union backlash if we see large numbers of eastern European workers freezing out the UK workers."
Lean added that since 1 May, when 10 European states joined the EU, there had not been an influx of foreign workers to the UK.
But he said there was evidence that European subcontractors want to come to the UK and tender at lower prices.
He said: "The eastern European firms are trying to infiltrate our market. Under the new freedom of movement rules, the eastern European firms can employ workers in their countries while servicing contracts in the UK."
Lean said the firms paid lower rates to workers and undercut UK firms at the bottom of the subcontract chain.
Amicus national construction officer Paul Corby said the issue of foreign workers was at the top of the TUC agenda.
He said that he had lobbied the DTI and the Treasury to toughen up regulations governing foreign workers.
Corby said: "We don't want the wage agreements that we fought so hard to negotiate being undermined by the arrival and exploitation of cheap foreign labour."