In a dramatic, tense state Assembly committee hearing Wednesday that took some unusual turns, a California net neutrality bill that backers hailed as the “gold standard” for internet protections was “eviscerated,” its author said.

Congressional leaders had joined the fight over the bill by Sen. Scott Wiener, D-San Francisco, highlighting the vital importance of internet regulation in the nation’s largest economy and the center of its tech and entertainment industries.

In a bipartisan 8-0 vote, the state Assembly Communications and Conveyance Committee forced amendments into SB822, stripping the Wiener bill of provisions that would have given the state the strongest prohibitions against discriminatory treatment of internet traffic in the country.

Wiener introduced his bill Jan. 3 in reaction to a Federal Communications Commission vote in December to overturn Obama-era regulations that required internet service companies to treat all web traffic equally. Supporters of Wiener’s bill — who included House Minority Leader Nancy Pelosi — hoped California would lead the charge for net neutrality standards in the country. But opponents warned that state-by-state legislation could lead to conflicting regulations for internet service providers, and instead preferred federal legislation by Congress.

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The committee, led by Assemblyman Miguel Santiago, D-Los Angeles, issued amendments to Wiener’s bill late Tuesday night, giving the public only a few hours to review the recommendations before the Wednesday morning hearing. Then, in a rare twist, the committee voted on the changes before Wiener was given a chance to speak against them.

This chain of events riled the senator, who was visibly upset after the vote.

“What the committee just did was outrageous,” Wiener said at the hearing. “These amendments eviscerated the bill — it is no longer a net neutrality bill. I will state for the record ... I think it was fundamentally unfair.”

Among the committee’s recommendations was to permit a controversial internet service provider practice called “zero rating,” where some websites and apps don’t count against a consumer’s data allotment. Opponents view zero rating as a backdoor way of discriminating against online services that don’t strike free-data deals with broadband and wireless companies. But proponents say the subsidies help lower-income communities access data services.

After the changes were forced into the bill, Wiener asked to withdraw it — a move that would have likely killed the proposal because of an upcoming June 29 deadline to pass all policy bills.

In response, Santiago said he was “disappointed” in Wiener’s decision.

Arms folded, Santiago addressed Wiener, sternly stating that he fully supports a net neutrality bill, and saying that the committee’s amendments were intended to set a foundation for future conversation. In a statement after the hearing, Santiago said he was “concerned” by the federal rollback of the Obama-era rules.

“Make no mistake,” he added, “the industry supports Trump’s actions and will do everything they can to sue and block implementation of net neutrality in California. When that happens, we will fight back.”

The bill’s future is now uncertain. SB822 moves to the Assembly Privacy and Consumer Protection Committee, but Wiener can still table the bill if it remains, as he called it, “mutilated.”

Critics of the move immediately accused Santiago of gutting the bill to please his donors, which include AT&T and Charter Communication, a cable broadband provider which serves parts of California. Both contributed $4,400 apiece to his campaign fund in recent months, and both oppose the bill. In April, Charter gave $10,000 at Santiago’s behest to a Los Angeles Police Department charitable initiative.

AT&T is a major contributor to the California Democratic Party, giving $175,000 this year alone, while Charter Communications gave $137,000. The California Cable Telecommunications Association, whose members include Charter and Comcast, donated $245,000 in the past six months.

Ernesto Falcon, legislative counsel at the Electronic Frontier Foundation, who consulted with Wiener on the bill, said Wednesday’s hearing was a “setback” in California’s fight to restore net neutrality protections.

California “is not as progressive as people assume,” he said. “I don’t think Santiago reflects upon the rest of the Assembly, but it does show the reach of the money.”

Santiago could not be reached Wednesday for comment.

House Minority Leader Nancy Pelosi, D-San Francisco, had sent a letter to Santiago on Monday urging him to pass “comprehensive protections” in the state. Her intervention elevated California’s net neutrality fight to the national level. Rep. Anna Eshoo, D-Palo Alto, sent a similar letter to Santiago on Tuesday.

After the vote, Pelosi’s spokeswoman, Taylor Griffin, said the congresswoman was “disappointed” with the committee’s actions.

“It is our hope that the state legislature will find a solution to safeguard Californians from the Trump FCC’s misguided net neutrality decision and secure California’s rightful place as a national leader in the fight for an open internet for all,” Griffin said.

Wednesday’s hearing came a few days after Wiener and Sen. Kevin de León, D-Los Angeles, announced amendments that would make Wiener’s SB822 work in tandem with de León’s SB460. The senators aimed to prevent infighting over which version of net neutrality might pass. Instead, they hoped to advance a comprehensive net neutrality package.

But the committee refused amendments to merge the bills and instead opted to hear them separately. De León pulled his bill from the hearing, and Santiago noted his absence.

“I’m very disappointed in the outcome,” de León said in a statement, adding that he remains committed to working on a net neutrality bill with Wiener.

Mike Montgomery, executive director of CalInnovates, an advocacy group which counts AT&T as a backer, is among the critics of Wiener’s bill who don’t support state-by-state legislation. While he said he was surprised at the dramatics in Wednesday’s hearing, he said the bill was “flawed” and “drafted in a way that we couldn’t support.”

“It wasn’t good for the consumer,” he said, saying that the zero-rating ban would negatively affect lower-income families and communities of color.

Wiener last week called CalInnovates an “AT&T-funded astroturf group.”

After the hearing, Wiener told The Chronicle that he will continue to “have conversations with the legislature” on this issue.

“California should be leading the way on protecting net neutrality, and instead we have a fake net neutrality bill, and that is a terrible state of affairs,” he said. “It is my hope that we can right this ship and turn it back into a strong net neutrality bill.”

Trisha Thadani and Melody Gutierrez are San Francisco Chronicle staff writers. Email: tthadani@sfchronicle.com, mgutierrez@sfchronicle.com Twitter: @TrishaThadani, @MelodyGutierrez