A California judge has ordered Visa and MasterCard to refund hundreds of millions of dollars of currency conversion fees. Judge Ronald Sabraw of California Superior Court said the 1 percent fee was not properly disclosed.

The ruling would require the companies to refund the currency conversion fees charged to all California consumers since Feb. 15, 1996. An attorney representing consumers said the amount could reach $800 million.

In making his ruling, the judge conceded that Visa and MasterCard have saved consumers millions by charging much lower currency conversion fees than other forms of payment. But he said that was "immaterial."

The credit card companies said they would appeal the decision and many analysts said they expected the California Court of Appeals to overturn Sabraw's finding. Sabraw's ruling followed a six-month trial in Oakland.

A similar case against American Express was recently filed on behalf of California consumers.

Another, potentially more far-reaching case is about to go to trial in New York federal court. In that case, giant retailers including Sears and Wal-Mart allege that Visa and MasterCard force merchants to take their debit as well as credit cards. Opening arguments are scheduled for April 28.

The currency conversion case is ironic in that few consumers are even aware that they were charged a fee for the conversions -- and many may have paid much more than one percent. The credit card companies do not itemize the fee on their statements and many banks routinely tack on another one or two percent, which might or might not appear as separate charges, depending on the bank.

Consumers will have to dig out their service agreements to find out if they are paying an addition fee to the bank that issued their credit card.

Both Visa and MasterCard are technically associations that provide transaction services to the banks who actually issue credit cards to their customers. The final decision on currency conversions and other fees rests with individual banks.