Seven U.S. senators, Brian Schatz of Hawaii among them, have written to President Donald Trump expressing concern that the United States has not conducted freedom of navigation operations in the contested South China Sea since October.

China continues to militarize the region, in the view of many U.S. officials, raising fears the Asian nation could disrupt what amounts to almost 30 percent of the world’s maritime trade that transits annually through the South China Sea, representing about $1.2 trillion in ship-borne trade bound for the United States.

“As you know, the United States is the only nation with a formal freedom of navigation operations program, or FONOPS, under which the United States has regularly conducted operations since 1979 on a global basis,” the senators wrote. “We strongly support the principle that the United States should ‘fly, sail and operate wherever international law allows,’ and that FONOPS are essential elements of larger U.S. strategy to safeguard freedom of navigation and overflight in the Asia-Pacific.”

The group said in the letter dated Wednesday that it was “encouraged” by the statement made by Adm. Harry Harris, commander of U.S. Pacific Command, at an April 27 Senate Armed Services Committee hearing, “that he expects new FONOPS to take place soon.”

In addition to Schatz, Sens. Bob Corker, Jack Reed, Edward Markey, Benjamin Cardin, Cory Gardner and Marco Rubio signed the letter.

Harris was asked during the committee hearing what the new Trump administration should look at in terms of policy in the South China Sea.

“I’ve made clear to this committee and in other testimonies to other committees that I’m a supporter of freedom of navigation operations,” Harris said.

Such operations can include sailing within 12 nautical miles of Chinese man-made islands that the United States contends are not sovereign territory under international law. The region’s reefs, shoals and islands also have competing claims by other countries.

Harris told the Senate Armed Services Committee that China has “militarized the South China Sea.”

“If you look at a graphic of Fiery Cross Reef, you’ll see a 10,000-foot runway, weapons emplacements, fighter aircraft hangars and barracks for troops,” Harris said. “Clearly, that facility, which is 700 acres, a military facility — all of that capability doesn’t exist to rescue the odd fisherman that gets lost out there.”

The seven senators are urging the Trump administration “to take necessary steps to routinely exercise freedom of navigation and overflight in the South China Sea.”

U.S. Pacific Fleet commander Adm. Scott Swift said in Singapore recently that the halting of freedom of navigation operations in the South China Sea is temporary, Bloomberg reported.

“We just went through a change in administration,” the news agency quoted Swift as saying. “I am not surprised that process has continued in a dialogue as the new administration gets its feet on the ground and determines where would be appropriate to take advantage of these opportunities and where we may want to wait.”