Support for Medicare for All is rapidly gaining momentum in Congress—and insurance investors are starting to get nervous.

Health insurance stocks tanked on Wednesday as Rep. Pramila Jayapal (D-Wash.) introduced comprehensive Medicare for All legislation with the backing of more than 100 House Democrats and major progressive organizations, including America’s largest nurses’ union and national consumer advocacy groups.

“The S&P 500 Managed Health Care Index plunged as much as 4.9 percent, the most since Dec. 6, led by UnitedHealth Group Inc., Humana Inc., and WellCare Health Plans Inc.,” Bloomberg reported after Jayapal unveiled her bill during an event on Capitol Hill. “Insurers UnitedHealth and Cigna Corp, which also own the country’s largest pharmacy benefit managers, were both down about four percent.”

Jayapal quickly made clear that she has no sympathy for the insurance industry, tweeting in response to the news, “Sorry not sorry.”