The leaders of X, Meta, Snap, TikTok and Discord have been called to testify before a Senate Judiciary hearing about online child sexual exploitation.

Sens. Dick Durbin, D-Ill., and Lindsey Graham, R-S.C., said Monday that they had issued subpoenas to the CEOs of X, Discord and Snap. The senators said they expected Meta CEO Mark Zuckerberg and TikTok CEO Shou Zi Chew to testify voluntarily, based on conversations they said had been occurring between committee members and the companies.

In a joint statement, the senators said they were seeking to compel the executives to testify at a hearing scheduled for Dec. 6, where they would “have their chance to explain their failures to protect kids.”

But Linda Yaccarino of X, Jason Citron of Discord and Evan Spiegel of Snap had been less cooperative, according to representatives for the senators.

A representative for Durbin said that X and Discord had refused electronic service of the subpoenas and that the senator’s office had engaged U.S. Marshals to serve them.

“After repeated refusals to appear during several weeks of negotiations, subpoenas have been issued,” the senators said in a news release. “In a remarkable departure from typical practice, Discord and X have further refused to cooperate by accepting service of the subpoenas on behalf of their CEOs, requiring the Committee to enlist the assistance of the U.S. Marshals Service to personally serve the subpoenas.”

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Wifredo Fernandez, head of U.S. and Canada government affairs at X, said the company is working to comply with the subpoena.

“We have been working in good faith to participate in the Judiciary committee’s hearing on child protection online as safety is our top priority at X,” he wrote in an email. “Today we are communicating our updated availability to participate in a hearing on this important issue.”

Meta declined to comment. Discord and Snap did not immediately respond to requests for comment.

Meta, TikTok, Discord, X and Snap have all faced scrutiny over the spread of material depicting the exploitation of children and the use of the platform by adults to groom minors.

In a review of court cases, NBC News identified 35 cases over the past six years in which adults were prosecuted on charges of kidnapping, grooming or sexual assault that allegedly involved communications on Discord. 

Investigations from other news outlets have similarly found that other social media platforms continue to be used for child exploitation.