Alaska Gov. Bill Walker on Sunday signed into law Senate Bill 54, which strengthens a wide range of criminal sentences but could face a legal challenge from the American Civil Liberties Union of Alaska.

The law, rolling back portions of last year's criminal justice overhaul, went into effect at 12:01 a.m. Monday, said Grace Jang, the governor's communications director.

Walker signed the bill in his office, without ceremony, to get it into law as quickly as possible, said Jang. The bill was transmitted to the governor Nov. 21, leading to several days of review by the Department of Law and the governor, Jang said.

The Law Department recommended that the governor sign it, Jang said.

"The second it reached his desk, he wanted to get on the books," Jang said.

Walker said in a statement Monday afternoon that some portions of the legislation might need to be addressed in court. But he called the law "an important first step" to give tools back to law enforcement agencies.

Among the highlights, Walker said, is that presumptive sentencing ranges for first-time Class C felony offenses are changed from a probationary sentence to the possibility of up to two years in jail.

Passed by the Legislature earlier this month, the law changed portions of Senate Bill 91 that was passed last year to reduce the state's costly reliance on prisons and increase supervision for people out on bail. Alaskans outraged over crime frequently blamed SB 91.

The ACLU says SB 54 has "serious constitutional issues." The bill increased penalties for first-time Class C felonies without increasing them for first-time Class B felonies — meaning that those sentences would be identical.

There are constitutional requirements that sentences be proportionate to the crime and "bear a substantial relationship to legislative policy," the ACLU argued in a Nov. 9 letter to senators.

Casey Reynolds, communications director for the ACLU of Alaska, would not say at what point the group would sue.

"I'm uncomfortable laying out our legal strategy," he said on Monday. But the ACLU "will stand up and defend the constitutional rights of Alaskans."

"It's sad the Legislature is comfortable passing and the governor is comfortable signing laws they know are unconstitutional and expect citizens to fight for their right in court to get them back," Reynolds said.

The Department of Law, in a Nov. 22 letter to Walker describing the new law, said the "statute will likely survive any constitutional challenge."

The agency said in a written statement on Monday that SB 54 would likely lead to litigation that will be expensive for the department.

"The Department of Law would have preferred to avoid using its limited resources on unnecessary litigation by having the Legislature fix the bill in conference committee," said the statement, emailed by Cori Mills, a spokeswoman for the agency.