An airline pilot union is calling on the U.S. government to temporarily ban cargo shipments of lithium batteries, saying they represent a serious safety hazard.

The Air Line Pilots Association (ALPA), which represents pilots in the U.S. and Canada, asked that the U.S. government prohibit shipments of lithium batteries on all cargo and passenger flights until measures are taken to insure that such shipments are safe. The proposed ban on the batteries, which are widely used in electronic devices like phones and computers, would not prohibit passengers from carrying batteries on planes.

“The evidence of a clear and present danger is mounting. We need an immediate ban on these dangerous goods to protect airline passengers, crews, and cargo,” said Mark Rogers, director of ALPA’s Dangerous Goods Programs,KD476, in a press release.

During the last two months, there have been three incidents where fire or smoke on aircraft was caused by shipments of lithium batteries. Those incidents were detailed in a letter that ALPA sent to Cynthia Douglass [CQ], acting deputy administrator of the Pipeline and Hazardous Materials Safety Administration of the Department of Transportation.

On August 14, the crew of a plane that landed in Minneapolis received a warning of smoke in the plane’s forward cargo compartment. When fire crews opened the compartment, they found flames coming from a container filled with electronic cigarettes, each containing a lithium-ion battery. In another incident in July, a container filled with lithium-ion GD761 batteries on a flight to Santo Domingo, Dominican Republic, was found smoking and smoldering.

In the third incident, which took place in June, a burned package containing a lithium-ion bicycle motor was discovered when cargo handlers unloaded a plane in Honolulu.

ALPA said all three incidents recall a 2006 incident where lithium TD347,Inspiron 6400 battery，Inspiron E1505 battery  caused a fire on board a UPS plane that injured three crew members and damaged cargo.