A bipartisan trio of U.S. Congressmen on Monday unveiled new legislation that would permanently ban illicit versions of fentanyl, the powerful synthetic painkiller that has helped fuel the nation’s opioid epidemic and death toll.

The proposed bill, introduced by Democrat Chris Pappas and Republicans Dan Newhouse and Ted Budd, comes days before a temporary ban on chemical copycats of fentanyl known as analogs expires on Friday.

Fentanyl, also spelled fentanil, is a powerful opioid used as a pain medication and, together with other medications, for anesthesia. It is also used as a recreational drug, sometimes mixed with heroin, cocaine, or methamphetamine, and its potentially deadly overdose effects can be neutralized by naloxone.

Fentanyl, which is 100 times more potent than morphine, is classified as a Schedule II drug, meaning it is highly addictive but has a medicinal purpose, typically to treat intense cancer pain.

But chemists largely based in China have created numerous slightly altered versions of the drug, which along with actual fentanyl have flooded U.S. streets and contributed to nearly 500,000 U.S. opioid overdose deaths over two decades.

To combat these illicit versions, the DEA previously clamped down by individually placing each illicit new fentanyl analog into Schedule I, the same legal category for drugs like heroin which are deemed to have no medical use.

In 2018, the DEA came up with a new approach, using its emergency powers to schedule all copycat illicit versions of fentanyl broadly into Schedule I as a single class, effectively banning them.

That authority has remained in place, thanks to repeated temporary extensions from Congress, which has yet to act on a long-term solution over concerns that a permanent ban could stifle scientific research into fentanyl analogs.

Chris Pappas said that his proposed bill contains provisions that he hopes will address researchers’ concerns by making it “less onerous and more streamlined” for scientists.

The new legislation introduced on Monday is not expected to pass before the DEA’s latest temporary emergency scheduling of fentanyl analogs expires.

However, Pappas told Reuters that lawmakers are looking into another temporary extension as part of a broader spending bill until a permanent solution is reached.