American Airlines and other carriers are facing possible fuel shortages at some airports, industry representatives said.

American told its pilots to conserve fuel by using a single engine while taxiing if the plane allows for that, the airline said.

“We are aware of fuel supply issues at some airports, predominantly across the western U.S., affecting a number of carriers,” American said in a statement Monday. It said the airline has had “minimal operational impact” so far.

The company said the issue was largely caused by a shortage of truck drivers and fuel trucks, and in some cases, pipeline allocations also are contributing to the issue. It said it has not had to cancel flights.

Read more: The Washington Post