More than 40 foreign operators of Boeing 737 planes may be using vehicles with an issue that could pose safety risks, an American agency has warned. The U.S. National Transportation Safety Board said on Monday that operators may be using planes with rudder components that could cause the issue.

The National Transportation Safety Board is issuing “urgent safety recommendations” for some Boeing 737s—including the embattled 737 MAX line— warning that critical flight controls could jam.

The National Transportation Safety Board issued urgent safety recommendations to Boeing over a steering defect related to its 737 planes, adding its growing list of woes.