MADISON, Wis. -- The state Assembly has decided against voting on a bill toughening drunken driving laws even after it approved a similar measure and the Senate passed it unanimously earlier Thursday.

Democratic Assembly leaders said in a press release issued late Thursday night that they needed more time to work out what they called minor differences.

Assembly Speaker Mike Sheridan, a Democrat from Janesville, said the bill could be passed in a special session. Thursday was the last scheduled day for the Legislature to be in session this year.

Lawmakers had been working on the measure for months and a very similar version passed the Assembly unanimously two months ago.

A fourth-offense drunken driving conviction would be a felony in some cases, instead of just a misdemeanor, under a bill passed by the state Senate earlier Thursday.

Backers of the measure the Senate passed Thursday said it gets tough on drunken driving in Wisconsin, even though first offenses remain a traffic violation. Wisconsin is the only state where that's the case.

Under the bill, a first offense would be a crime only if someone under age 16 is in the car.

The increased penalties under the bill passed would be paid for by increasing from $50 to $90 a fee paid by drunken drivers whose licenses are suspended or revoked.

Gov. Jim Doyle has said he supports the bill and is expected to sign it.