OMHex, the Nordic exchange operator, is preparing for a legal battle after rejecting claims from a group of Finnish banks and brokerages that it owes them €5m ($6.04m) in value added tax payments.

On Friday, 22 firms said they were to sue OMHex's Finnish subsidiaries - Hex Integrated Markets and the Finnish Central Securities Depository - to recover VAT payments made for trading and clearing services between 1995 and 2000.