NEW YORK (AP) — Sen. Charles Schumer urged regulators to “use extreme caution” when reviewing the proposed acquisition of No. 3 cell carrier Sprint Nextel by Japan’s Softbank, saying the Japanese company’s use of Chinese networking equipment could open up U.S. networks to snooping and hacking.

The New York Democrat sent letters Friday to the Treasury Department and Federal Communications Commission, both of which are reviewing Softbank Corp.’s offer to buy 70 percent of Sprint Nextel Corp. for $20.1 billion.