Supreme Court Chief Justice John Roberts on Tuesday temporarily blocked a congressional subpoena that seeks information on how the classified advertising website Backpage.com screens ads for possible sex trafficking.

The order came hours after Backpage CEO Carl Ferrer asked the high court to intervene, saying the case threatens the First Amendment rights of online publishers.

A federal appeals court ruled 2-1 on Friday that the website must respond to the subpoena within 10 days. Roberts said Backpage does not have to comply with the appeals court order until further action from the Supreme Court. He requested a response from the Senate Permanent Subcommittee on Investigations by Friday.

The Senate panel has tried for nearly a year to force Backpage to produce certain documents as part of its investigation into human trafficking over the Internet.

After the website refused to comply, the Senate voted 96-0 in March to hold the website in contempt. The vote allowed the Senate to pursue the documents in federal court, marking the first time in more than two decades that the Senate has enforced a subpoena in court.

A federal district judge sided with the Senate last month, rejecting arguments that the subpoena was unconstitutional, overly broad and burdensome. The U.S. Court of Appeals for the District of Columbia Circuit agreed.