With thousands of flights canceled in Europe recently — more than 13,000 in May alone — it’s time to revisit something called EU Regulation 261.

If your flight in Europe gets canceled, most airlines will offer you a voucher, and many travelers accept it. But under EU 261, the airline must also offer to rebook you or provide a full cash refund.

Airlines don’t always volunteer this information, so it’s important to know your rights. And remember, this rule applies to any passenger traveling on any airline — including U.S. airlines — departing from an EU airport.