The outbreak of African swine fever in China has prompted leaders of the House Energy and Commerce Committee to write a letter to the FDA voicing concerns about the disease’s potential repercussions on the U.S.’ heparin supply.

The letter, written to FDA Acting Commissioner Ned Sharpless, expresses worries about the nation’s reliance on China for pig intestines, which heparin is derived from. China currently holds half the global pig supply, the lawmakers said.

Heparin, an intravenous anticoagulant, is an essential product in hospitals and is the only anticoagulant used in the U.S. for kidney dialysis and open heart surgeries, the committee said.