WASHINGTON (Reuters) -The outgoing head of the Federal Communications Commission said a massive Chinese-linked cyber-espionage operation against U.S. telecoms firms known as "Salt Typhoon" is a "clarion call" to address significant telecommunications security issues.

"Salt Typhoon is a clarion call that reminds us that the security of our networks is absolutely vital for our national and economic security," FCC Chair Jessica Rosenworcel, who steps down on Monday, said in a Reuters interview.

"We've got to make some changes ... We have to figure out how it happened. We have to figure out the extent of the incursion, and then, most importantly, we have to take action to make sure it never happens again."

Senator Ben Ray Lujan, the top Democrat on a telecom subcommittee, said China's alleged efforts likely represent "the largest telecommunications hack in our nation's history."

Verizon and AT&T have said they were impacted by Salt Typhoon but said last month their networks are now secure.

The FCC voted on Thursday to require telecommunications to have cybersecurity risk management plans. Rosenworcel predicted there would be other threats from malicious actors and nation states in the future, and called for more to be done to make the networks more resilient.

Incoming FCC Chair Brendan Carr said the Salt Typhoon attack "represents an unacceptable risk to our national security" but criticized the commission action.

"We should be taking a series of actions that will restore America's deterrence and harden our networks going forward," Carr added.

Under Rosenworcel, the FCC has taken steps to crackdown on Chinese telecoms including seeking to boost security of information transmitted across the internet after Washington said a Chinese carrier misrouted traffic. The FCC is also reviewing rules governing undersea cables that carry most internet traffic.

The FCC voted in 2022 to prevent Huawei, ZTE and other Chinese companies from winning approvals for new telecommunications equipment. Congress in December approved $3.1 billion for U.S. telecom companies to remove equipment made by Huawei and ZTE from American wireless networks.