Suffolk lawmakers unanimously approved a bill Tuesday night that makes it a misdemeanor for adults to allow underage drinking in their homes instead of a violation.

The amendment to the so-called social host law, sponsored by Legis. Tom Cilmi (R-Bay Shore) and Legis. Monica Martinez (D-Brentwood), would allow police to better crack down on drinking as graduation and prom season heats up, sponsors and police officials said.

Police officers currently have to witness the underage drinking because it is classified as a violation under the law, Police Commissioner Timothy Sini said.

“This will enhance our ability to enforce the social host law,” Sini said. “It sends an important message out to the community that we won’t tolerate underage drinking.”

Cilmi said the Suffolk County Police Department “is handcuffed from adequately enforcing the law.”

Martinez, a former school administrator, said the legislation adds accountability for hosts.

“I have witnessed firsthand the peer pressure that many of our students are faced with on a daily basis, including the act of social drinking,” she said.

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The law passed unanimously 18-to-0, but not until after a lengthy debate. Some lawmakers worried the bill would catch parents who were simply unaware drinking was going on.

Legis. William Spencer (D-Centerport) noted his son’s pending high school graduation party. While he planned to check students for alcohol, he worried he could be held accountable if someone sneaked in a drink.

“They’re extremely creative,” he said.

Legis. Lou D’Amaro (D-North Babylon) said he worried minors would falsely accuse adults.

“I’m concerned about an improper allegation against somebody, where now they’re charged with a crime,” he said.

The county’s law, unchanged by the legislation considered Tuesday, says it’s a crime to “knowingly allow the consumption of alcohol” by a minor or “fail to take reasonable corrective action” once they became aware.

The penalty under the law would be a maximum fine of $500 for the first offense and $1,000 and up to a year imprisonment for second and subsequent offenses.

In other action, good-government advocates praised a proposed public campaign finance referendum for Suffolk legislators, which would give a 4-to-1 match on donations of up to $150 for candidates who opt in.

The bill would also extend legislators’ terms from two to four years. Susan Lerner, executive director of Common Cause New York, said she supports both the matching funds and the longer terms.

“This allows a candidate to run a competitive race without have to chase the top dollar,” she said.

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Legislators are expected to vote in July whether to put the referendum on the ballot in November.

Republican lawmakers though were skeptical because the law doesn’t cover countywide races and questioned whether candidates would opt in.

The campaign funds would be paid for with video lottery terminal funding from a yet-to-be-opened casino. County lawmakers also unanimously passed a $220 million budget for Suffolk County Community College, that includes a $200 increase in annual tuition, a 4.4 percent increase.

Other increased fees total about $98 a year. The community college’s budget, a 2.2 percent increase in spending over the prior year, still has to be passed by school trustees.