Under a new law, karaoke businesses and restaurants that allow customers to "bring your own booze" will have to order customers to stop drinking at midnight instead of 2 a.m.

Legislators introduced the new law to curb late-night noise around businesses that let customers supply their own alcoholic beverages and do not fall under county liquor commissions.

Businesses that do not have liquor licenses can still be fined for alcohol violations.

Gov. Linda Lingle allowed Senate Bill 2545 to become law as Act 198 without her signature on Tuesday.

A Honolulu Liquor Commission official said investigators will start enforcing the law right away.

Before the new regulation, BYOB establishments could operate the same hours as regular bars, from 6 a.m. to 2 a.m. the next day.

Some were surprised last week by the decree.

"It’s a horrible idea," said Dave Gagnon, who was with friends Friday night at Toma Enterprises, a karaoke business in Moiliili. "It’s going to hurt places like this."

"It’s definitely going to make a difference," said Alan Morimoto, who works at Toma. "Our business is only starting to get busy like at 9 or 10 o’clock."

He said "prime time" starts after 9 p.m. and continues until 1 a.m. on weekdays and 2 a.m. on weekends.

"A lot of people don’t sing unless they drink," he said, adding that they might have to close at midnight to force people to stop drinking.

His wife, Rieko Morimoto, whose family has owned the business for about 20 years, said, "If no more drink, we got to close up."

The number of BYOB establishments on Oahu is unknown because they are not regulated.

Anna Hirai, acting Honolulu commission administrator, said penalties for not complying will range from a written reprimand to a $2,000 fine for businesses.

It is unlikely that individuals drinking after hours will be cited unless they are underage, she said.

The law also creates a new class of liquor license on Oahu, which would allow an establishment to let patrons drink what they brought in until 2 a.m.

But Hirai estimates it could take a year before the commission can come up with rules and set fees for that license.

"We won’t be issuing any of the new liquor licenses for a little while," she said. "The rule-making process is a very expensive one for the agency."

Hirai said the fee for the license must be calculated to cover the cost of policing establishments with the new BYOB license.

The new law also allows customers to bring home any leftover wine, liquor or beer that they bought or brought.