Chinese telecom giant ZTE agreed Tuesday to plead guilty to violating U.S. laws that restrict business with Iran, and will pay the largest criminal fine ever in an export case — nearly $900 million. 

Federal officials called the plea and fines "a new high-water mark in enforcement efforts." 

ZTE, the fourth-largest smartphone vendor in the U.S., admitted it shipped millions of dollars worth of U.S.-sourced products to Iran illegally, sales "that were approved at the highest levels of the company," federal officials said. Employees were asked to sign non-disclosure agreements about the sales and used an e-mail system that automatically deleted messages.

The company also admitted that employees lied to federal investigators who inquired about the sales.

"ZTE Corporation not only violated export controls that keep sensitive American technology out of the hands of hostile regimes like Iran’s — they lied to federal investigators and even deceived their own counsel and internal investigators about their illegal acts,” said Attorney General Jeff Sessions. "This plea agreement holds them accountable, and makes clear that our government will use every tool we have to punish companies who would violate our laws, obstruct justice and jeopardize our national security."

ZTE sells phone handsets to AT&T, T-Mobile US, and Sprint.