A new High Court ruling will be passed to decide when those exposed to asbestos should receive compensation.
The legal battle will determine whether insurers are liable for damages from a victim's first exposure to the deadly substance or from when they suffer its affects.
Unite is the trade union backing those workers that have been exposed asbestos and, they say, the insurance industry is trying to avoid its liabilities.
Derek Simpson, joint general secretary of Unite, said: "It is a sickening scenario, and we will fight every step of the way to see that insurers are not allowed to pass the buck and dodge their responsibilities."
Mr Simpson described the "millions of pounds" at stake as Asbestos-related disease is the biggest cause of work-related deaths in the UK.
People that are exposed to asbestos can contract a type of cancer called mesothelioma, which can follow exposure to the substance by 25 to 40 years.
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