Home secretary David Blunkett gave details of the draft corporate killing bill on Tuesday, along with a timetable for enacting it.
Stephen Kay, HSE branch chairman of Prospect, said: "We are concerned at the message that the government is sending out by the failure to resource prosecution work – it suggests that the HSE is not serious about prosecution and that it doesn't matter if negligent employers get away with it."
The Construction Confederation welcomed the news on Tuesday that individual directors would not be targeted under the bill. Andy Sneddon, the confederation's health and safety director, said an attempt to penalise individuals would "cut across the collective responsibility that should exist in organisations to manage safety".
Instead, a firm that is convicted of gross negligence would be liable for an unlimited fine and would hold a criminal record.
A Construction Confederation spokesperson said a full consultation on the issue was required. More details of the bill are expected to be announced in the autumn.
Ucatt general secretary George Brumwell urged the government to make parliamentary time for a debate on the subject with a view to taking action.