The use of electronic cigarettes is now banned in all U.S. national parks. The National Park Service announced Monday that e-cigarette vaping is banned anywhere cigarette smoking is prohibited.

A National Park Service internal memo issued Sept. 10 says the rule is meant to “protect employees and park visitors from the health hazards and annoyances associated with exposure to environmental tobacco smoke, commonly known as secondhand smoke, which is a known human carcinogen.”

The Las Vegas Review Journal notes, the memo references studies that claim vapor exhaled from e-cigarettes have nicotine at a level one-tenth that found in secondhand smoke.

Banning e-cigarettes in the same areas as tobacco smoking, the memo says, was made “out of an abundance of caution in light of the scientific findings and uncertainty to date, and in the interest of equity.”

A Park Service spokesman defended the outdoor ban, telling U.S. News and World Report that a park superintendent could prohibit outdoor vaping citing safety reasons, such as preventing forest fires.

A National Park Service spokesman told U.S. News that if a park superintendent decides to restrict outdoor smoking for reasons such as preventing forest fires, that restriction would now also apply to electronic cigarettes.

American Vaping Association Trade Group President Gregory Conley said the new restrictions are wrong and should not be enforced.

“Outdoor smoking bans in parks can at least somewhat be justified by the risk of fires, but vapor products pose no more of a fire risk than a cellphone battery,” he told U.S. News. “This behavior is shameful and any enforcement of the ban will constitute a great misuse of government resources. The National Park Service should leave ex-smokers alone and let them camp and hike in peace.”

According to a 2014 study in the International Journal of Wildland Fire, a sharp decrease in the number of outdoor fires was connected to cigarettes in recent decades. The study hypothesized the drop is a result of improvements in detecting a fire’s origin as well as a decline in the national smoking rate.