A law meant to stop sex trafficking — lauded by Ivanka Trump, signed into law by her father in April, and championed by members of Congress who have been working for years to crack down on bad actors like Backpage.com — is now being challenged by tech company advocates and internet rights groups who say it violates the First Amendment.

The tech industry-funded nonprofit Electronic Frontier Foundation (EFF) will urge a federal judge Thursday to stall enforcement of the law, known as FOSTA-SESTA, which holds websites accountable if they knowingly facilitate criminal activity like human trafficking that happens on their platforms. (FOSTA is short for the Fight Online Sex Trafficking Act, and SESTA is the Stop Enabling Sex Traffickers Act.)

While FOSTA-SESTA was hailed as a victory by many advocates for survivors of sex trafficking, some in the tech community have pushed back on the law over concerns that the government is moving to require tech companies to censor the internet.

Prior to passage of FOSTA-SESTA, tech companies had widely been protected against being held liable for any illegal content or business conducted on their platforms.

"FOSTA attacks online speakers who speak favorably about sex work by imposing harsh penalties for any website that might be seen as 'facilitating' prostitution or 'contribute to sex trafficking,'” EFF said in a press release.

EFF’s lawyer arguing the case, Robert Corn-Revere, has previously represented Backpage.com, a website that was shut down by the Federal Bureau of Investigation, and its CEO Carl Ferrer, who pleaded guilty in three state courts to money laundering and conspiracy to facilitate prostitution.

Sen. Rob Portman, R-Ohio, one of the architects of the law, said this is not a free speech issue but instead about protecting victims of sex trafficking.

“Victims of this abhorrent crime can finally have their day in court and the websites that knowingly facilitate sex trafficking are being shut down and being held liable for their actions,” he said. Portman led a 20 month U.S. Senate investigation that found Backpage complicit in trafficking. He says the shuttering of Backpage.com, which he called the “industry leader in sex trafficking,” is a victory.

Prior to passage of FOSTA-SESTA, Backpage’s defense in response to charges that it proliferated prostitution and trafficking was that it's not responsible for ads posted on the site. That argument is based on Section 230 of the 1996 Communications Decency Act, which says online service providers cannot be held liable for content provided by third parties.

After the law passed, Craiglist shut down its “personals” section.

FOSTA-SESTA is a definitive turning point for the internet and holds platforms accountable in an unprecedented way. EFF’s constitutional challenge is championed by those who complain FOSTA-SESTA could create an advantage for bigger companies with the technology and money to make sure that their platforms comply with the law.

“Every effort to turn platforms into content police favors the well-established, well-capitalized platforms,” said Mike Godwin, senior fellow at the nonprofit research firm R Street Institute and the former general counsel for Wikimedia Foundation. “If you are a startup, you now have to hire a thousand lawyers and contract workers to screen content.”

But longtime advocate for survivors of child sex trafficking, Mary Mazzio, said EFF’s constitutional challenge is disingenuous.

"The child sex trafficking survivors, along with the community of adult survivors, nonprofits, and NGOs who fought for the passage of FOSTA-SESTA, are dismayed to find that EFF, which began a disinformation campaign prior to the bill’s passage, has continued its relentless assault on any attempt to hold websites accountable that engage in criminal conduct," Mazzio said.