Over half a dozen U.S.-loaded ethane vessels, originally bound for China, have stalled around the U.S. Gulf Coast after Washington requested U.S. exporters seek licenses to ship the shale gas to the top buyer, according to trade sources and ship tracking data on Friday.

Around half of all U.S. ethane exports head to China, and the halt in flows has pushed ethane prices lower on worries of domestic oversupply and is likely to cut into profits of top ethane producers. 

Energy Transfer and Enterprise Products Partners, two of the largest ethane producers and exporters, have warned the disruptions could impact their exports. The U.S. Commerce Department has also denied some vessels emergency authorization requests to export to China.

Liberia-flagged STL Qianjiang, which loaded at Energy Transfer’s Nederland terminal for China’s Satellite Chemical, was anchored off the coast on Friday in the Gulf, according to LSEG and Kpler ship tracking data. 

Energy Transfer, which produces ethane by extracting it from natural gas and then exports it from terminals along the Gulf Coast, said it received a letter from the U.S. Commerce Department on June 3 requiring the company to apply for a license to ship ethane to China.