On Thursday, the FDA (Food and Drug Administration) sent warning letters to five companies that make e-cigarettes or components for the plastic and metal devices, saying some make unproven health claims, but also said the agency wants to work with them to clarify what’s legal.

In the letters, the FDA said the companies are violating the Federal Food, Drug and Cosmetic Act, including unsubstantiated claims and poor manufacturing practices.

The five companies are: Las Vegas-based E-Cig Technology Inc., E-CigaretteDirect LLC of Colorado, Ruyan America Inc. in Minneapolis, Florida-based Gamucci America, and Wisconsin-based Johnson Creek Enterprises LLC.

Kimree, as a leading electronic cigarette manufacturer, encourages the industry group to work with the FDA to ensure the safety and effectiveness of the devices to help people quit smoking traditional cigarettes through usually expensive clinical trials.