The 19 companies, with a combined workforce of 3,000, raided by German authorities, are preparing to sue both the German and Hungarian state, the association’s lawyer Boldizsar Toth told the press.
The firms said they had complied with the rules of a Hungarian-German intergovernmental agreement on working in Germany.
But they nevertheless found themselves subject to raids, the seizure of documents, frozen bank accounts and arrests.
The German authorities said they were acting to clamp down on black labour, alleging that Hungarian companies were bringing cheap labour gangs to Germany.
Berlin said Hungarians could only offer services in Germany if 25 percent of their total revenues came from operations in Hungary. The German authorities claimed this was not the case.
German police carried out two major crackdown operations in May 2004 and April 2005.
The German courts have since ruled in favour of the Hungarian firms in half of the cases and thrown out the other half.