His signature came a day after the measure was approved by the state House and Senate, which are led by his fellow Republicans.
The measure prompted weeks of pro-labor protests by thousands of people amid a national debate over union rights, keyed by a similar bill passed in Wisconsin and signed by the governor there.
The Ohio bill prevents unions from negotiating wages but not health care, sick time or pension benefits. It also eliminates automatic pay increases and bans strikes. It applies to teachers, nurses and many other government workers, including police and firefighters, who were exempt in the Wisconsin measure.
Kasich, a first-term governor, has said his $55.5 billion state budget counts on unspecified savings from lifting union protections to fill an $8 billion hole. He and his GOP colleagues argue the bill will help city officials and superintendents better control their costs at a time when they, too, are feeling budget woes.
Democrats opposed the measure but offered no amendments to it. Instead, they delivered boxes containing more than 65,000 opponent signatures to the House labor committee's chairman.
Many Democrats, along with other opponents, have vowed to lead a ballot-repeal effort if the measure passes. Backers of a ballot challenge have 90 days after Kasich signs the bill to gather 231,148 valid signatures from at least half of Ohio's 88 counties to get it on the ballot.
"We are disappointed with its passage; we expected it out of this administration," said Austin Keyser with the Shawnee Labor Council. "We're gearing up for the referendum now."
Keyser said the bill Kasich signed Thursday is an attack on the working class.
“It does nothing to help fix the budget and creates a divide in our communities,” Keyser said.
The process of gathering necessary signatures is expected to start next week, Keyser said.
If the thousand signatures are gathered and certified, Keyser said, SB5 will not go into effect, "until after the November election, when the voters have a chance to veto what the legislature has done. I do not think we will have any problem gathering the signatures; I think we'll double it," Keyser said.
State Rep. Dr. Terry Johnson, R-89, who voted against SB 5 when it was before the House, said it is now up to Ohio voters to decide if they will accept the new law.
"Obviously, this has been a highly contentious and even divisive matter. That is regrettable, as we need now more than ever to unite and work for the benefit of all."
The bill signing comes two days after a House labor committee added GOP-backed revisions that make it more difficult for unions to collect certain fees.
The committee changed the bill to ban automatic deductions from employee paychecks that would go to the unions' political arm. They also altered the measure to prevent nonunion employees affected by contracts from paying so-called "fair share" fees to union organizations.
Unions argue that their contracts cover those nonunion workers and that letting them not pay unfairly spreads the costs to dues-paying members.