The National Institute for Clinical Excellence is expected to make its recommendations next week but has indicated that it will advise that the drug should not be used.
Ucatt said this is despite there being proof that the drug increases the survival rates and the quality of life of many sufferers.
Alan Ritchie, general secretary of Ucatt, said: “It is sickening that Nice could even consider a postcode lottery on easing the suffering of people dying from a horribly painful disease, developed at work through no fault of their own.
“If mesothelioma was a disease of the chattering classes, rather than of manual workers, I am sure the decision would be different.”
The union has estimated that by 2050 more than 186,000 people will have died from asbestos-related diseases.