WASHINGTON — A vaping industry group sued the U.S. government on Wednesday to delay an upcoming review of thousands of e-cigarettes on the market while several cases of lung injuries possibly linked to vaping are being investigated.

The legal challenge by the Vapor Technology Association is the latest hurdle in the Food and Drug Administration’s yearslong effort to regulate the multibillion-dollar vaping industry, which includes makers and retailers of e-cigarette devices and flavored solutions.

Meanwhile, Minnesota health officials have identified four cases of severe lung injury that could be connected to vaping, similar to what could be dozens more cases in nearby Wisconsin and Illinois.

The Minnesota Department of Health said it’s unclear whether these cases are somehow connected. While officials said they don’t yet know the exact products used, both nicotine and marijuana products have been reported.

“There are still many unanswered questions, but the health harms emerging from the current epidemic of youth vaping in Minnesota continue to increase,” the department’s medical director and state epidemiologist, Dr. Ruth Lynfield, said in a statement Tuesday. “We are encouraging providers and parents to be on the look-out for vaping as a cause for unexplained breathing problems and lung injury and disease.”

The announcement said some were hospitalized for “multiple weeks, with some patients being admitted to the intensive care unit.” They came in with symptoms including shortness of breath, fever, cough, vomiting, diarrhea, headache, dizziness and chest pain.

Dr. Emily Chapman, chief medical officer at Children’s Minnesota, which reported the four cases, said in a statement that such cases are tricky to diagnose because they can start off looking like a common infection before leading to more serious complications.

Cases in Wisconsin and Illinois

In Wisconsin, health officials are still investigating increasing reports of people with severe lung disease who say they’ve recently vaped or “dabbed,” which involves inhaling marijuana products.

As of August 8, there are 12 confirmed cases and 13 more under investigation in the state. These latest numbers now include “older age groups,” whereas previously they had only received reports of teens and young adults.

“All patients reported vaping prior to their hospitalization, but we don’t know all the products they used at this time,” Andrea Palm, the state’s Department of Health Services secretary-designee, said in a statement last week. “The products used could include a number of substances, including nicotine, THC, synthetic cannabinoids, or a combination of these.”

Health experts have pointed to a variety substances in e-liquids they worry may harm cells or contain “dangerous chemicals,” but the full extent of e-cigarettes’ short- and long-term risks are yet unclear. A number of counterfeit and adulterated products have also hit the market, which may have other additives or ingredients. It is unclear whether that plays a role across these cases.

And in Illinois, six young people have been hospitalized for severe breathing problems after vaping, and five more are being investigated as of August 9, according to a statement issued last week by the Illinois Department of Public Health.

The department said it’s working with local health departments, other states, the US Centers for Disease Control and Prevention, and the US Food and Drug Administration to look into which vaping products were used and where they were obtained.

“Without this information, we have been unable to conclusively determine which chemicals the individuals may have been exposed to,” the department said.

‘Otherwise normally healthy’

Thomas Haupt, a respiratory disease epidemiologist with Wisconsin’s Department of Health Services, told CNN earlier this month that the cases in his state were young people who were “otherwise normally healthy, and they were coming in with severe respiratory illnesses, and in some cases, they actually had to go to the intensive care unit and were placed on ventilators.”

The lung disease initially looked like it was caused by an infection, “but every test has come back completely negative,” Haupt said.

Wisconsin’s cases were largely in the southeastern part of the state, Haupt said. This borders the northeastern part of Illinois, where the state’s initial patients were hospitalized.

Dr. Ngozi Ezike, director of the Illinois Department of Public Health, previously told CNN that her team has many unanswered questions but has “talked to people from Wisconsin” and is gathering data and running tests. A number of cases occurred in people with “no known lung problems or previously diagnosed pulmonary issues,” Ezike said.

On the legal front

In Washington, the vaping group argued that the latest deadline of next May to submit products for review could wipe out many of the smaller companies. The lawsuit was filed in U.S. District Court in Kentucky.

E-cigarettes first appeared in the U.S. more than a decade ago and have grown in popularity despite little research on their long-term effects, including whether they can help smokers quit cigarettes.

San Francisco-based Juul is among 800 member companies of the vaping association.

A 2009 law that gave the FDA power over the traditional tobacco products did not mention e-cigarettes. And it wasn’t until 2016 that the agency expanded its own regulations to include the devices. But since then FDA regulators have repeatedly pushed back the timeline, at one point until 2022, to begin review the legions of vaping products that have come to market.

Frustrated by the delays, anti-tobacco groups including the Campaign for Tobacco-Free Kids sued the FDA to speed up the process. In June, a federal judge sided with the groups and set a deadline of next May for all companies to submit their products for federal review. The FDA has until next month to appeal the decision.

The vapor group’s lawsuit said the FDA has now set five different deadlines.

“It is time for FDA to stop moving the goalposts and changing the rules in the middle of the game to the detriment of our manufacturers and small businesses,” said Tony Abboud, the group’s executive director, in a statement.

Vaping executives have long said that most companies will not be able to afford to conduct large, expensive studies needed for FDA review. Only products that meet FDA standards would be permitted to be sold.

The FDA declined to comment on the lawsuit.