If you plan on entering the United States by plane, make sure your mobile devices are charged first.

Passengers on direct flights to the United States must now be able to turn on their electronic devices during the security check, the Transport Security Administration says.

"Powerless devices will not be permitted onboard the aircraft," the TSA announced in a statement issued Sunday. The TSA already examines electronic devices, but screeners may now ask travellers to turn on those devices as part of the process. "The traveller may also undergo additional screening," the TSA said.

U.S. head of Homeland Security Jeh Johnson said last week that he ordered the additional check, but did not indicate why.

"We are sharing recent and relevant information with our foreign allies and are consulting the aviation industry," he said in a statement. "Aviation security includes a number of measures, both seen and unseen, informed by an evolving environment."

The TSA did not say how screeners will deal with electronic devices that are still in their original packaging, including gifts being brought into the United States.

A representative from Transport Canada said additional security measures will also be implemented for Canadian flights, but did not go into specifics.

"Transport Canada has been monitoring the situation closely, and intends to implement enhanced security measures soon," Roxane Marchand, media relations advisor for Transport Canada, said in an email to CTVNews.ca.

"Any additional security measures are expected to have a minimal impact on passengers," she said. "For security reasons, Transport Canada cannot provide specific details of security measures."

Twitter reaction to the announcement was mostly outraged, annoyed or sarcastic.

Last week, the Department of Homeland Security announced it will beef up security measures at foreign airports. The move came after a U.S. counterterrorism official said al Qaeda is developing an undetectable explosive device to smuggle onto commercial airliners.