WHEN THE VOTE finally came in the wee hours of Tuesday morning on a vigorously debated police reform bill, the measure easily cleared the state Senate by a 30-7 margin. But one dissenting vote stood out on legislation prompted by a nationwide surge of attention to the issue of police brutality toward black Americans. Sen. Nick Collins, a South Boston Democrat whose district extends through much of Dorchester and Mattapan and is one of just three majority-minority seats in the 40-member Senate, joined four other Democrats and two Republicans in voting against the bill, which sets out a sweeping set of reforms, including a ban on chokeholds and the use of tear gas, and system for certifying all police officers in the state.

In a statement posted Tuesday evening on Twitter, Collins said he supports many provisions in the bill, including the ban on chokeholds, facial recognition technology, and tear gas, a requirement to collect racial disparity data on traffic stops, and ending automatic prosecution of teenagers as adults. But he called the bill’s most controversial element — a provision imposing new limits on the protection police officers enjoy from civil lawsuits — “problematic.”

While many black activists strongly support new limits on “qualified immunity,” Collins, who is white, cited concerns about the provision from minority law enforcement groups and said the language, which would apply to all public employees, “has the high likelihood of being used disproportionately against minority government employees in many sectors.”

Collins, who did not return messages, said in his statement his no vote “was a decision I did not take lightly.”

State Rep. Russell Holmes, the former head of the state’s Black and Latino Legislative Caucus, whose Dorchester and Mattapan House district overlaps with Collins’s Senate district, said he was “very surprised” by his colleague’s vote.

On Tuesday, Holmes said he called Collins, who explained his concerns about the qualified immunity provision. The bill would limit protection from civil lawsuits to situations in which “no reasonable defendant could have had reason to believe that such conduct would violate the law.”

Holmes said he told Collins it looks as if he opposed the whole bill, including “police certification and a commission on what to do about structural racism.”

“It doesn’t just look like you voted against qualified immunity,” Holmes said he told Collins.

In his statement, Collins also raised another criticism leveled by police unions — that they weren’t part of any conversations to help craft the bill and that the legislation was not the subject of a public hearing.

Collins also pointed out that Rep. Carlos Gonzalez, chairman of the Black and Latino Legislative Caucus, cautioned the Senate against straying from “core reforms” outlined in a 10-point plan the group issued, which did not include the qualified immunity provision.

Collins’s district is one of only three out of 40 Senate districts where minority residents make up a majority of the population. (The other two are the neighboring Roxbury-based district represented by Sen. Sonia Chang-Diaz, and the Springfield district represented by Sen. James Welch.) According to the Census Bureau’s 2018 American Community Survey, the population of Collins’s district is 40 percent black, 34 percent white, 15 percent Hispanic, and 8 percent Asian.

Jonathan Rodrigues, a Mattapan constituent of Collins’s, was one of several voters who took to Twitter to criticize his stand on the bill.

“Our city is massively impacted by issues of police brutality misconduct,” Rodrigues said in an interview. He called it “disappointing” that a senator representing a district that is majority of color didn’t support the bill.

“Starting today the search for a viable challenger next term is on. Inbox me,” Rodrigues tweeted on Tuesday. “His vote against systemic reforms of police is simply disqualifying.”

A Dorchester resident, Samuel Pierce, has qualified to challenge Collins on the September Democratic primary ballot, but he doesn’t appear to have an active campaign website. No Republicans are running in the heavily Democratic district.

The police reform bill now moves to the House, where Speaker Robert DeLeo had said he would schedule a public hearing before the chamber takes up the legislation. State House News Service reported on Wednesday that House leaders will instead accept written testimony via email through Friday morning on the Senate-passed bill.

Collins said he’s hopeful that the House will produce a more “thoroughly vetted bill,” for the Senate to consider. “I look forward to voting for a package that brings about thoughtful and meaningful reform to address police misconduct, holds unfit officers accountable, and addresses racial injustice in our Commonwealth,” he wrote.