The U.S. has issued another NOTAM, this time covering Curaçao and nearly the entire southern Caribbean Sea between Venezuela and Puerto Rico. A NOTAM is a notice countries can issue to alert airlines that flying through a certain airspace may be “dangerous.” In this new NOTAM, the U.S. warns that unidentified aircraft may be operating in the area — its way of referring to military aircraft, such as fighter jets.

With this new NOTAM, flights passing through the region will be even more affected, which may include routes connecting Brazil to the U.S. and Central America.