A Belfast firm of solicitors is suing a major trade union for allegedly breaching a 10-year contract to provide legal services to its members.
Agnew Andress Higgins has also accused the Amalgamated Transport and General Workers' Union of fraudulent misrepresentation and negligence.
The firm is understood to be seeking hundreds of thousands of pounds in what it claims are unpaid fees and loss of profit.
According to legal papers in the case, which opened at the High Court in Belfast on Monday, Agnew Andress Higgins provided advice and representation to the ATGWU from 1985.
Services were supplied to members of the union in personal injury claims and employment law issues, documents state.
But the firm alleges the ATGWU breached the terms of a 10-year contract it says was entered into in 2004.
Agnew Andress Higgins was to continue to receive the same number of members' personal injury claims, which was then averaging at over 400 a year, it is claimed.
Around this period it agreed to provide legal services in industrial tribunal cases free of charge, except for the most sensitive or complex, papers submit.
In its claim, however, the firm alleges its referrals in personal injury claims dropped from 418 in 2004 to 46 in 2007.
The document alleges the firm was told by a senior representative of the union - which has since merged with Amicus to form Unite - that the introduction of a new law practice onto its panel of solicitors would not affect the number of referrals.
It also states partners in Agnew Andress Higgins were told the downturn in personal injury cases was due to an administrative error which would be rectified immediately.
Setting out the claim for damages, the paper contends: "The defendant has been unjustly enriched in that the plaintiffs have carried out free legal work for the defendant and its members involved in employment law cases."
The hearing, in front of Mr Justice Weatherup, is expected to last for five days.
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