The filters are not mandatory, so check with your airline.

Best to check with your airline each time you fly.

Here's the official advise, check with your airline to be sure.

Check with your airline before agreeing to pay anything extra.

Check with your airline or travel company and allow plenty of time to get through security.

Check with your airline to see if it offers in-flight Internet.

Please check with your airline or travel company before travelling.

Anyone planning to fly should check with their airline before going to the airport.

In short you really have to check with your airline and also take into account what you're doing on the way back.

Affected customers should check with their airline to see whether the flights have been paid for.