Bravo to FDA Commissioner Dr. Scott Gottlieb for giving a timely ultimatum to e-cigarette makers last week: These firms can either crack down on underage use of their harmful products or face serious consequences for their bottom lines.

The challenge now for Gottlieb is to back up that tough rhetoric with action, particularly if e-cigarette firms respond with vague assurances or by targeting Gottlieb himself. The Food and Drug Administration commissioner is a Trump appointee and serves in an administration that has elevated regulatory rollback as a priority.

The fast-growing industry, which has one firm valued at $15 billion, may well mount a lobbying campaign to cow Gottlieb. He should stay the course and ensure that protecting new generations from nicotine addiction remains a top agency priority. While Gottlieb is well-regarded, a previous decision that gave the e-cigarette industry a regulatory reprieve raises troubling questions about his resolve.

The ultimatum from the FDA came on Sept. 12 as part of a “series of critical and historic enforcement actions” to stem e-cigarette use in kids. Juul, the leading manufacturer by far, and four other firms have been given 60 days to prove they can keep these products out of underage hands. If they can’t, they could face severe consequences, including a move that could cripple their business — market removal of the sweet-flavored nicotine products very young users find so appealing.

The bold action is merited. Gottlieb has rightly called e-cigarette use by teenagers an “epidemic.” Use by high-school students rose from 1.5 percent in 2011 to nearly 12 percent in 2017, according to a national youth tobacco survey by the U.S. Centers for Disease Control and Prevention (CDC). A Minnesota breakout of the survey showed that 19.2 percent of high school students here have used or tried e-cigarettes in the past 30 days, up 49 percent from 2014.

It’s easy to see how e-cigarettes’ design attracts young users. The sleek Juul device looks like a flash drive to store computer data. It’s also easy to hide in a classroom or in a home. Videos on YouTube and photos posted by users of other social media underscore how these products, which deliver a nicotine vapor, have been embraced by a young crowd. In Minnesota, consumers generally must be 18 to buy, though some cities have moved to raise the age to 21.

Concrete steps and hard deadlines are critical in the plans Juul and other firms provide to Gottlieb before the end of the year. Sensible remedies already outlined by 11 public health-minded U.S. senators in an April 18 letter should form the framework of the response. These include strengthening age verification for direct sales on the company websites and strategies to do the same on eBay and other third-party online sellers.

Another step is aggressively protecting the companies’ trademarked names and logos, and preventing them from appearing on T-shirts, hoodies and other products. FDA rules already prevent traditional cigarette brand names from being used this way. The industry should voluntarily end this type of marketing rather than wait for the FDA to step in.

A myth about e-cigarettes needs to be clearly understood. They appear to be less harmful than traditional cigarettes, though long-term research is lacking. But less harmful is still not good. Nicotine can “harm adolescent brain development,” and the vapor may contain other cancer-causing chemicals, according to the CDC.

Critics of Gottlieb’s initiative may contend that it will simply result in young people smoking regular cigarettes. That’s a false “either-or” claim. The crackdown will help ensure that fewer young people get addicted to nicotine. More must be done to prevent all types of cigarette use, but the FDA initiative is a logical step — if Gottlieb carries it through.