The U.S. Department of Transportation has banned the use of electronic cigarettes on commercial flights.

Transportation Secretary Anthony Foxx announced the new rule Wednesday, calling it an effort to prevent vulnerable passengers from being exposed to harmful chemicals. The measure applies to flights into and out of the United States, along with domestic and international carriers.

Previously, passengers were prohibited from packing the devices in their checked bags, but were allowed to bring them in carry-ons as long as the devices and batteries were not charged aboard the aircraft. It was unclear whether the previous rules prohibited inhaling from the vaporizers on flights, something DOT sought to clear up with Wednesday’s ‘final rule’.

The new rule effectively treats electronic cigarettes the same as traditional tobacco cigarettes, which are banned from use on U.S. flights.

“This final rule is important because it protects airline passengers from unwanted exposure to aerosol fumes that occur when electronic cigarettes are used onboard airplanes,” Foxx said in a statement. “The Department took a practical approach to eliminate any confusion between tobacco cigarettes and e-cigarettes by applying the same restrictions to both.”

DOT said the devices are a concern because they contain a number of harmful chemicals, potentially exposing children, older passengers and those with respiratory issues to aerosol in an enclosed space.

The department said the new rule eliminates any confusion over whether previous regulations applied to e-cigarettes, and it applies to all forms of electronic cigarettes including: electronic cigars, pipes and “devices designed to look like everyday products such as pens.”