WASHINGTON — The Senate’s top Democrat on Monday asked the Federal Communications Commission to consider whether two major Chinese telecommunications companies should be barred from operating in the United States.

Senator Chuck Schumer of New York, the Democratic leader, along with Senator Tom Cotton, an Arkansas Republican, cited national security concerns in a letter asking the commission to review the licenses that give the two companies, China Telecom and China Unicom, the right to use networks in the United States.

In the letter, they said that the two Chinese government-linked telecom operators could use that access to “target” Americans’ communications. And they warned that the companies could reroute communications traveling on their networks through China. The text of the letter was obtained by The New York Times.

The request by the two senators shows how leaders in Congress are willing to apply more pressure to Chinese technology firms even as President Trump seems open to pulling back on some of the restrictions as part of the trade negotiations with China. The focus on two previously untouched firms shows that efforts to restrict Chinese technology firms are expanding.