Yvonne Ambrose, trying in vain to hold back tears, testified inside a hushed Senate hearing room Tuesday about the last day of her daughter’s life. Desiree Robinson was 16, and was being prostituted on Backpage.com when a man outside Chicago beat her, choked her and cut her throat on Christmas Eve 2016.

“Desiree didn’t know what Backpage.com was or the harm that would come from this website,” Ambrose told the Senate Commerce Committee. She said her daughter’s alleged killer scanned Backpage.com because he knew it was “the site to go to in order to find young, underaged girls to have sex with.” He knew the ad with the words “New girl in town looking to have fun” indicated an underage girl, Ambrose said. “Her pictures that were posted and moderated by Backpage.com were the reason for her demise.”

After leading a two-year investigation into online sex trafficking which focused largely on the classified ads website Backpage, Sen. Rob Portman (R-Ohio) introduced a bill which he and 28 co-sponsors believe will close a crucial loophole of immunity for sites which host prostitution-related advertising: an amendment to the Communications Decency Act which shields web hosts from liability for content posted by others. The bill, titled the “Stop Enabling Sex Traffickers Act,” would add language that exempts “sex trafficking of children” and “sex trafficking by force” from Section 230 of the communications act, which was written in 1996 and credited by many with allowing the Internet to flourish without threat of costly litigation or regulation. It would also clarify that state and local prosecutors can pursue violators under federal law, as could plaintiffs in state civil courts.

The bill also would amend the federal law which already prohibits sex trafficking to define “participation” in an illegal venture as “knowing conduct by an individual or entity, by any means, that assists, supports or facilitates” sex trafficking. Those terms are frighteningly vague to advocates of a free Internet, and two witnesses testified Tuesday that such changes to the law would cause websites to stop policing their own sites, for fear of “knowing” something illegal, discourage people from launching websites at all, or open web hosts to a raft of lawsuits.

Online sex trafficking just keeps growing, despite law enforcement’s efforts to curtail it. The National Center for Missing and Exploited Children receives about 9,000 to 10,000 reports of suspected child sex trafficking each year, and has already received 9,700 this year, according to Yiota Souras, the center’s general counsel. Of those reports, more than 80 percent of the incidents have occurred online, she said. And when victims seek to hold websites responsible, they “are being deprived of their day in court against every entity that knowingly supported their trafficking,” Souras said, “because of the legal protections provided to these entities under current law.”

“The fact that incidents of human trafficking are increasing,” said Portman, “in this country, in this century, it’s an outrage. The selling of human beings online is the dark side of the Internet. It can’t be the cost of doing business.”

The Senate, and the House in a similar bill introduced by Rep. Ann Wagner (R-Mo.), was moved to action after a series of court rulings in cases involving Backpage. When the website has been sued by young women who were sold for sex there, or prosecuted by law enforcement authorities in Illinois and California, judges have ruled that Section 230 of the CDA grants Backpage immunity because it is merely hosting the sex-related content, not creating it. “Judges across the country have made it clear,” Portman said, “it is Congress’s responsibility to fix this law.”

Liz McDougall, Backpage’s general counsel, said the company had no comment on the proposed law.

But one of the original authors of the law, Sen. Ron Wyden (D-Ore.), testified against changing the law. “We made it crystal clear” in 1996, Wyden said, “that nothing in Section 230 protects against violation of criminal law. If law enforcement needs more resources…let’s give them what they’ve gotta have.” But he added, “I just believe this legislation being considered today is the wrong answer.” He felt that small businesses would be reluctant, or unable, to enter the marketplace if they had to begin their Internet life worried about lawsuits.

The Internet Association, which represents tech giants such as Google, Facebook and Amazon, weighed in against the bill as well. Abigail Slater, the association’s general counsel, said the association’s companies are “100 percent committed to stopping Internet sex trafficking,” and noted that Google and others developed software called “Spotlight” which combs through millions of online ads and flags potential child victims. But she said the proposed term “knowing conduct” could be used by a prosecutor to go after a website which only knows that its users are communicating, not what the content is, and civil lawsuits could take a similar approach. Slater said the association prefers a carefully crafted law enabling victims to pursue their traffickers through civil actions.

“It is not hard to imagine that opportunistic lawyers will bring a deluge of frivolous litigation,” Slater said in written testimony submitted to the committee, “targeting legitimate, law-abiding intermediaries.” Souras responded that “knowing conduct” is “not just simply a blanket notice-type standard,” and would not open the door to lawsuits.

Eric Goldman, a law professor at Santa Clara University with a specialty in Internet law, said the bill opens up the question of when did a website know it had something questionable on its site, and what did it do about it. He said large companies may be able to handle these dilemmas, but that would be problematic for small companies without easy access to lawyers, and some companies may want to avoid getting involved altogether.

Sen. Richard Blumenthal (D-Conn.), a co-sponsor of the bill, told Goldman, “I have a higher opinion of the industry than you do.” He said, “Most companies want to do the right thing. This law will give them more impetus to do it.”

But it was Ambrose who took the discussion from the theoretical to the current reality. She is suing Backpage for wrongful death for its role in her daughter’s slaying. As part of that suit, Ambrose obtained documents which showed that Backpage used a contractor in the Philippines to generate more business for its adult services ads, which now appear in the “dating” section of the site.

“I would not wish this pain on my worst enemy,” Ambrose told the committee, about having to bury her child. “And I pray that Desiree’s life can make a difference so that no one else has to endure this pain.”

Afterward, Ambrose said she was nervous. Not about testifying under bright lights with high-powered senators watching. She said she was nervous about whether or not the bill will actually pass.

Nearly every senator who spoke on the Commerce committee voiced their support for the bill, but no vote was scheduled on passing it out of committee.