Portable chargers and power banks might be useful additions to your carry-on luggage, but they’re also a potential fire risk. Now Southwest Airlines is tightening rules around their use on board aircraft.

The TSA already bans rechargeable and non-rechargeable lithium batteries for phones and laptops from checked baggage. Carry-on baggage is fine, but Southwest Airlines will soon require those chargers to be outside of all bags and visible while in use during the duration of the flight.