The Supreme Court declined Tuesday to block subpoenas issued to Backpage.com by a Senate committee that is investigating its alleged role in facilitating child sex trafficking.

The Center for Missing and Exploited Children has identified Backpage as a primary online marketplace for child sex trafficking ads on the internet.

The website was subpoenaed nearly a year ago by the Senate Permanent Subcommittee on Investigations. When the subpoena -- which was issued in October 2015 -- went unanswered, the Senate took a rare move and held Backpage in contempt of Congress, which hadn't been done since 1995.

But Backpage and its CEO, Carl Ferrer, have refused to comply with the subpoena, arguing that the First Amendment protects the company from complying with the Senate's demands.

But on Tuesday, the nation's highest court denied Backstage's request to block the subpoena. Justice Samuel Alito recused himself.

Related: Senate holds Backpage.com in contempt, sparking likely free speech fight

Backpage declined to comment on the court's action.

Lawyers for Ferrer had argued in court papers, "This case highlights a disturbing -- and growing -- trend of government actors issuing blunderbuss demands for documents to online publishers of content created by third parties (such as classified ads) in a manner that chills First Amendment rights."

Stephen Vladeck a CNN contributor and law professor at the University of Texas called the case "an absolute quagmire in First Amendment doctrine."

"The whole fight is about whether and to what extent the First Amendment protects online publishers of third-party content (like Backpage)," Vladeck said.

Related: A lurid journey through Backpage.com

Backpage functions much like Craigslist, but it's been known to be more permissive for adult content.

It was the target of CNN investigations in 2011 and 2012. Numerous lawmakers and regulators have been after the company in recent years, attempting to shut down the site's adult content section where much of the suspected child sex trafficking activity occurs.

American Express (AXP), Mastercard (MA) and Visa (V) stopped allowing cardholders to make payments on the site in 2015.

Mastercard and Visa acted after an Illinois sheriff estimated Backpage was making about $100 million per year from adult advertising, and he lobbied the credit card companies to take action.

Senators Rob Portman and Claire McCaskill are heading up the Senate investigation. The lawmakers have called Backpage "the most important player" in the commercial sex advertising market.

Backpage claims to combat human trafficking, saying that it screens posts for illegal activities. But a subcommittee investigation says Backpage actually aids sex traffickers by helping to shield them from detection.

For instance, the Senate investigators found Backpage screens posts before they appear online, and the site removes key words from ads that could tip off law enforcement officials to illegal activity.

Editor's note: This article has been updated to clarify the Supreme Court's action and to correct the spelling of Stephen Vladeck's last name.