The potential link was seen mostly in young vapers, FDA Commissioner Scott Gottlieb and Principal Deputy Commissioner Amy Abernethy said in a statement on Wednesday. The FDA said it has received 35 reports of seizures possibly related to e-cigarette use between 2010 and early this year, and is concerned those numbers could indicate a wider phenomenon.

“We want to be clear that we don’t yet know if there’s a direct relationship between the use of e-cigs and a risk of seizure,” Gottlieb told a House appropriations subcommittee at a hearing on the agency’s budget request.

The agency is raising the issue to encourage the public to report adverse events related to e-cigarettes to the FDA’s online portal. Seizures are a known risk associated with ingestion of nicotine liquids used in e-cigarettes.

The FDA has been particularly concerned about an epidemic of youth vaping associated with popular e-cigarettes made by Juul Labs Inc. and recently proposed to restrict sales of flavored products in retail stores. The agency said in its statement on Wednesday that in many of the seizure reports, it couldn’t identify a specific brand or sub-brand of device.

Shares of tobacco makers who are trying to diversify away from traditional cigarettes by embracing electronic devices declined on Wednesday. Altria Group, which has a large stake in Juul Labs, fell 3 percent to $55 at 1:02 p.m. in New York, while Philip Morris International Inc. declined 2.2 percent to $86.06.

An Altria spokesman declined to comment on the FDA alert. Juul spokesman Joshua Raffel said in a statement that the company has “robust safety monitoring systems in place and will vigilantly monitor for any evidence of safety issues.”

Philip Morris is seeking U.S. approval for IQOS, a heated-tobacco device that would compete with Juul’s e-cigarette and that is already sold in many countries. Altria has a deal to market IQOS if cleared for sale in the U.S.

“It’s clear this relates to usage reports on e-cigarettes currently available or used in the U.S.,” said Philip Morris spokesman Corey Henry. “Given that we don’t sell or market any e-cigarettes, or any nicotine-containing products, in the U.S., it’s not really our place to address adverse effects or quality issues reported to FDA on products that aren’t ours.”

In the reports the FDA received, some vapers reported a prior history of seizures and some reported they had used other substances such as marijuana or amphetamines along with e-cigarettes. DM