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WASHINGTON -- A Senate panel voted on Wednesday to hold the classified advertising website Backpage.com in civil contempt for failing to comply with a congressional subpoena into how it screens ads for possible sex trafficking.

The Homeland and Governmental Affairs Committee backed a resolution setting up a legal fight with the company. The full Senate must vote on the resolution.

Sens. Rob Portman, R-Ohio, and Sen. Claire McCaskill, D-Mo., sponsored the resolution after they said the company refused to comply with a subpoena last year. Holding the company in contempt would allow the committee to go to court to try to force Backpage.com to turn over documents about its screening practices.

Senate approval would mark the first time in two decades the chamber has voted to hold someone in contempt.

Related: New York State and Facebook Team Up to Fight Online Sex Trafficking

In a statement, a lawyer for Backpage.com said the company welcomed the vote. Steven Ross said the company does not believe Congress can compel an online publisher of third-party advertisements to produce the documents under the First Amendment.

Backpage.com "looks forward to a proper consideration of these important First Amendment constitutional issues by the judiciary — the branch of government charged with protecting the constitutional rights of all Americans," Ross said.