A cohort of 11 lawmakers, led by Illinois Sen. Dick Durbin, on Wednesday sent letters to both JUUL CEO Kevin Burns and Food and Drug Administration (FDA) Commissioner Scott Gottlieb regarding the youth appeal of the company’s vaping devices, which resemble flash drives and come in flavors including mango, fruit medley, and creme brûlée. Each JUUL pod, which lasts about 200 puffs, contains as much nicotine as a pack of cigarettes.

E-cigs cannot be legally purchased by minors, and JUUL representatives have repeatedly said they do not condone youth use of their products and limit their online sales to those 21 and older. Nonetheless, “Juuling” has become a widespread problem in schools, prompting the senators to assert in their letter to Burns that JUUL products are “undermining our nation’s efforts to reduce tobacco use among youth and putting an entire new generation of children at risk of nicotine addiction and other health consequences.”

The letters, which come just weeks after a study found that vaping may prompt young people to start smoking, were co-signed by senators Sherrod Brown, Richard Blumenthal, Chuck Schumer, Patty Murray, Tom Udall, Chris Van Hollen, Jack Reed, Ed Markey, Elizabeth Warren, and Tim Kaine.

The letter to Burns puts forth 12 questions the senators are looking for JUUL to answer by April 30. Topics include whether JUUL will discontinue its kid-friendly flavors, how many of its products are sold to children younger than 18, and what the formulas are for each of its different pods.

In addition to their potential appeal to kids, e-cigarette flavorings have been highlighted for their potential risk to human health. A 2015 study, for example, found they may cause a respiratory illness nicknamed “popcorn lung.” The Centers for Disease Control and Prevention also notes that some of the chemicals used in e-cigs may be cancer-causing.