An announcement is expected this week on compensation arrangements for sufferers of pleural plaques.
Campaigners have been pressing ministers for years to overturn a Law Lords ruling in 2007 which denied compensation to victims.
The construction workers union Ucatt claimed yesterday that the government was only planning to compensate victims who had already lodged a legal case before the Law Lords ruling in October 2007.
The union claimed the government was unwilling to pay compensation to public sector workers exposed to asbestos while employed in former nationalised heavy industries.
General secretary Alan Ritchie said: "The state employed these workers and exposed them to asbestos. Now the state must pay their compensation. A failure to do so is morally indefensible."
The union said there was 30 million worth of legally stayed pleural plaques cases, including many where insurance companies would have been liable to pay compensation.
Mr Ritchie added: "The government is intending to pay compensation, from an already severely overstretched public purse, to pleural plaques victims when it is the insurers who are liable. Why on earth are the insurers not being made to pay?"
The union said ministers were preparing to head off widespread criticism of its plans by proposing funding of a national centre for asbestos-related disease and a register for pleural plaques sufferers.
Mr Ritchie said: "The government has claimed they are looking beyond the pleural plaques issue. Instead, they are abandoning the vast majority of pleural plaques victims whose health has been damaged … This is the opposite of social justice, on which Labour was founded."