U.S. transportation regulators this spring plan to ban smokeless electronic cigarettes on airplanes, the Associated Press reported Friday, citing a letter from Transportation Secretary Ray LaHood.

Writing to Sen. Frank Lautenberg (D-N.J.), LaHood said his department  has been informing airlines and the public that it interprets smoking regulations to include e-cigarettes.

Lautenberg, who wrote the 1987 law that bans smoking on U.S. airplanes, had asked the DOT to clarify the rule.

E-cigarettes are plastic and metal devices that heat a liquid nicotine solution in a disposable cartridge, creating vapor the “smoker” inhales.