Whistleblower Zatko has claimed Twitter had misled regulators about its compliance with a 2011 settlement with the Federal Trade Commission over improper handling of user data.
The chair of the Senate Judiciary Committee and the panel's top Republican on Monday asked Twitter Inc Chief Executive Parag Agrawal to answer questions about a former company executive turned whistleblower who is set to testify.
Peiter "Mudge" Zatko, a famed hacker who served as Twitter's head of security until he was fired last year, will appear on Tuesday before the committee.
Senate Judiciary chair Dick Durbin and Republican Chuck Grassley asked Agrawal to answer questions by Sept. 26 including Zatko's allegations Twitter "turned a blind eye to foreign intelligence infiltration, does not adequately protect user data and has provided misleading or inaccurate information about its security practices to government agencies."
The senators said they had invited Agrawal to testify on Tuesday, but he had declined. Twitter declined to comment.
Durbin and Grassley outlined some concerns raised by Zatko, including potentially more than half of Twitter full-time employees having privileged access to company production systems. With that capability, several thousand employees can access sensitive user data, according to Zatko.
"... at the same time, Twitter reportedly lacks sufficient capacity to reliably know who has accessed specific systems and data and what they did with it," the senators wrote in a letter to Agrawal.
"With tens of millions of users in the US and hundreds of millions of users worldwide, your company collects and is responsible for vast troves of sensitive data," they wrote.
"If accurate, Mr. Zatko's allegations demonstrate an unacceptable disregard for data security that threatens national security and the privacy of Twitter's users."
'Personal and privacy concerns'
Zatko has claimed Twitter had misled regulators about its compliance with a 2011 settlement with the Federal Trade Commission over improper handling of user data.
Durbin, while speaking to reporters on Monday, said Zatko's claims were "a matter of grave personal and privacy concern."
Twitter has said the former executive was fired for "ineffective leadership and poor performance," and that his allegations appeared designed to capture attention and inflict harm on Twitter.