A $28 billion American industry selling intoxicating hemp gummies, seltzers and smokable flowers is fighting to survive a federal ban that Congress passed last year and, last month, delayed until Dec. 11.

The delay, tucked into the short-term government-funding bill that President Trump signed last month, pushed the effective date of what the industry calls the hemp THC ban from Nov. 12 to Dec. 11. Industry advocates and some lawmakers want Congress to use the extra weeks to regulate the products rather than wipe out the market, which is separate from the state-licensed marijuana business.

The market exists because of how Congress wrote the law. Marijuana and hemp are the same plant, cannabis. Marijuana is bred for high levels of THC in its flowers; low-THC hemp has historically been grown for fiber, food and wellness products, and farmers who pushed to legalize it long used the motto “rope, not dope.”

To give farmers a new cash crop, Senator Mitch McConnell, the Kentucky Republican, drove the legalization of industrial hemp through the 2018 farm bill. But the law defined hemp as having less than 0.3 percent of one specific form of THC, delta-9, by weight. A drink or a snack could meet that threshold and still contain more than enough THC to get a person high.

Unregulated and untested, hemp-derived THC spread across the country in vape oil, gummy candies, chips and sodas, sold in gas stations and convenience stores where even teenagers could buy it, alongside THC seltzers stocked by some Target stores. Some businesses began selling raw marijuana under the theory that its THC exists in a form called THC-A and becomes impairing delta-9 only when heated or burned. The products evaded state bans on recreational weed and undercut licensed, heavily taxed cannabis where marijuana is legal.

Dozens of states answered by regulating or banning the products themselves. Then Mr. McConnell moved to close the loophole he had opened, inserting a hemp THC ban late last year into the measure that ended the longest government shutdown in history.

Now people who built businesses on the loophole are waiting on Congress. In a commercial kitchen outside Raleigh, N.C., Nicholas Hohns runs a company whose signature product is potent THC gummies made with the main intoxicating compound in marijuana, a business he may soon have to give up.

It’s such a weird spot to be in. You worked 100 hours a week for the past four years and, yeah, you made some money. But now you might have nothing to show for it.

Mr. Hohns spoke to the Associated Press. Whether Congress will replace the ban with regulation before Dec. 11 is unclear; the delay passed only as part of a bill to keep the government open.