If you recently used your credit or debit card in a foreign country, you may get a refund of money you should never have been charged.

Whether you spent 2 weeks touring the ruins of Italy or two days seeing the sights in Canada, if you used plastic during your visit to any foreign country, your credit card company calculated the currency exchange rate.

But 6 years ago, some cardholders noticed a problem. The numbers on their statements didn't add up. They filed a class action lawsuit.

The currency conversion suit accused MasterCard, VISA, Diners Club and their partner banks of tacking on undisclosed currency exchange fees for every transaction and, in some cases, inflating the base exchange rates.

The lawsuit claims the hidden fees generated more than $3.5 billion for the credit card issuers. The credit card companies deny any wrongdoing, but agreed to settle out of court.

So who's eligible for a refund? Everyone who traveled outside the U.S. between February 1 of 1996 and November 8 of 2006 and made purchases, ATM withdrawals, cash advances or Internet transactions with a credit or debit card.

This applies to all international transactions using MasterCard, VISA and Diners Club. If you fall into this category - you have until May 30 to file a claim.

If you fit the criteria, you have three options. You can file a claim for a flat $25 refund if you spent less than $2,500 outside the country. You can request an estimated refund based on the typical foreign travel of more than a week and more than $2,500. Or you can get an estimated refund based on foreign travel or transaction.

For more information and claim forms, click here.