Lawmakers concerned about possible drug shortages amid the coronavirus outbreak are pressing pharmaceutical companies to bring manufacturing to the U.S.

Sens. Marsha Blackburn, R-Tenn., and Bob Menendez, D-N.J., are among lawmakers pushing for longer-term solutions. The senators on Wednesday introduced a bill that would funnel $100 million to develop U.S. manufacturing of drugs.

“When confronted with a serious challenge such as the coronavirus, it is important to take stock, look at lessons learned and build upon them in order to respond better the next time,” Blackburn said in a statement.

About 72% manufacturers of pharmaceutical ingredients supplying the U.S. are overseas, including 13% in China, according to FDA testimony last year. That could make U.S drug companies vulnerable to shortages if COVID-19 forces factories to shutter and shipments to the United States to stall, experts have warned.

The Food and Drug Administration said Tuesday it will suspend most inspections for food, drug and medical devices outside the country through April, potentially putting more strain on the system.

FDA Commissioner Stephen Hahn has said the agency has been in touch with more than 180 manufacturers of drugs. Only one, so far, has alerted the agency to a shortage. In testimony before the Senate Committee on Health, Education, Labor and Pensions last week, Hahn said he couldn’t disclose which drug it was, but said it was nonessential and alternatives were available.

Hahn also has said the FDA has been in touch with 63 manufacturers of medical devices and has found no reported shortages, though he acknowledged to senators in testimony a large demand for masks and fears about the U.S. stockpile.

The Blackburn-Menendez measure is at least the third legislative proposal addressing the issue.

Earlier this month, two Wisconsin congressmen, Democrat Mark Pocan and Republican Mike Gallagher, introduced the Medical Supply Chain Security Act, which could give the FDA the authority to identify sourcing locations for medical supplies.

Last year, Reps. John Garamendi, D-Calif., and Vicky Hartzler, R-Mo., introduced the Pharmaceutical Independent Long-Term Readiness Reform Act that would require the Department of Defense to purchase only American medicines and vaccines.

But some lawmakers are pushing for more urgent actions — and information. Specifically, they want to know what products are vulnerable to shortages. The FDA is not bound to disclose that information to the public.

“The problem we are facing is: What is the risk? We just don’t know,” Pocan said in an interview.

“The only entity that keeps track of that supply chain is the FDA. As I understand it, they consider it proprietary, so we don’t know.”

Pocan wrote a letter last week to drug manufacturers including AbbVie, Amgen, Bristol-Myers Squibb and Takeda to ask for more details around potential shortages as a result of COVID-109.

He has not heard back from any of those companies, an aide told CNBC.