Today, Hong Kong’s South China Morning Post reports that Beijing has been issuing threats to ExxonMobil, demanding that the U.S. firm terminate its exploration deal with state oil company PetroVietnam. The two energy companies plan to look for oil in the South China Sea in an area Vietnam claims. Hanoi’s position is based on the fact that the area is on its continental shelf and within its exclusive economic zone.

Beijing, however, also claims the site in question. In addition to asserting rights to Vietnam’s continental shelf, it claims the continental shelves of the Philippines, Indonesia, Malaysia, and Brunei. Moreover, Beijing appears to maintain that virtually all of the South China Sea is an internal Chinese lake due to the voyages by its mariners in ancient times. If adjudicated before an international tribunal, Vietnam would certainly prevail.

Up to now, Washington has adopted a passive attitude on the ludicrous Chinese claims. Yet if China’s views on its borders were respected, American vessels and aircraft would need Beijing’s permission to transit the South China Sea and Washington would thereby surrender its role as protector of international waters and airspace.

The Chinese have always threatened neighbors in order to enforce their outsized territorial claims. Now, it is threatening an American firm. It’s time for Washington to defend every nation’s right of passage-and the interests of its own businesses.

I believe we maintain carrier strike groups for this very purpose.