(Bloomberg) -- The leaders of the Senate Judiciary Committee sent a detailed list of questions to Twitter Inc. on Monday night, hours before the committee will hear testimony from whistle-blower Peiter Zatko, who has accused the company of failing to adequately protect data on its users. 

In a letter addressed to Twitter Chief Executive Officer Parag Agrawal, the senators wrote that Zatko’s allegations, if true, “demonstrate an unacceptable disregard for data security that threatens national security and the privacy of Twitter’s users.” 

“The disclosure paints a disturbing picture of a company that has fallen short of basic security standards in the technology industry, failed to adequately mitigate attempts by foreign governments to gain access to sensitive user information, and willfully misled government regulators,” wrote Judiciary Committee Chair Dick Durbin of Illinois and the panel’s top Republican, Chuck Grassley of Iowa. 

Zatko, also known as “Mudge,” spent two years as Twitter’s head of security before he was fired earlier this year. In a series of complaints, he alleged that Twitter failed to patch up significant security flaws and flouted promises to the US Federal Trade Commission.

Twitter declined a request for comment on Monday night.

The committee invited Agrawal to testify at the hearing on Tuesday, which is scheduled to begin at 10 a.m. Washington time, but he didn’t accept, according to the letter. The senators asked Twitter to respond to its questions by Sept. 26. 

The senators expressed concern about Twitter’s policies and procedures for protecting user data from “insider threats posed by foreign intelligence.” They pointed to the former Twitter employee who was convicted by a federal jury in August for acting as an unregistered foreign agent for Saudi Arabia. 

Twitter has denied Zatko’s claims and argued that he is a disgruntled former employee who was fired for poor management. 

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