Anchorage Mayor Dan Sullivan took a major step Monday toward sending the city's controversial labor law to the ballot box, vetoing the recent Assembly repeal of the law as well as a more labor-friendly substitute measure approved in its place.

Sullivan announced his decision to reporters early Monday afternoon. In one of his two veto messages, Sullivan wrote that "special interest objections to a few provisions do not constitute a sound reason to repeal the act."

Sullivan has made the law, known as Anchorage Ordinance 37, AO37 or the "Responsible Labor Act," a signature piece of his administration. Speaking to reporters at Monday's press conference, he also roundly rejected the terms of the substitute version of the law passed by the Assembly last week, which incorporated amendments requested by union representatives.

"It's not a compromise and does not represent anything resembling what we accomplished with AO37," Sullivan said.

Unless the Assembly takes action to override the veto at a special meeting Tuesday night, the original law will appear on the state ballot in November as a referendum. Last week, on both the repeal of the law and the substitute measure, the Assembly voted 7-4 -- one vote short of the eight votes required to override a veto.

In separate interviews Monday, none of the four Assembly members who opposed the repeal -- Bill Evans, Amy Demboski, Ernie Hall and Jennifer Johnston -- indicated they planned to change their positions.

"I'm weighing it all once again ... I'm not seeing a lot that's changing my mind," Hall said.

Evans, Johnston and Demboski all said they were standing by their positions and expect the issue to go to a public vote in November.

"I believe people have the right to vote on this issue," Demboski said.

The original labor law was introduced in February 2013 and includes provisions that eliminate the right to strike and prevent unions from seeking binding arbitration, as well as outsourcing some union jobs. In the year and a half since, the law has been through two court cases, and labor leaders gathered more than 20,000 signatures while campaigning for a referendum.

In May, Assembly member Jennifer Johnston sought to avoid a referendum vote by sponsoring a compromise measure that unions dubbed "AO-37 lite." Johnston, union representatives and members of the municipal attorney's office spent the next three months hammering out the details.

But Johnston did not support the measure that ultimately won Assembly approval.

"What passed Tuesday isn't much different than what's on the books," she said Monday, adding that she was in support of the mayor's veto.

Sullivan's veto message for the substitute measure also said it was a "far cry" from the original AO37 and "substantially less" than Johnston's original proposal.

Union representatives, meanwhile, argued that labor had agreed to the majority of the changes proposed by Johnston.

"We were only asking for three things to be left the same," said Gerard Asselin,the president of the Anchorage Coalition of Unions and a sergeant with the Anchorage Police Department. Those sticking points centered on provisions the unions said would give the city authority over staffing and scheduling decisions and remove some employees from collective bargaining units.

Asselin said Monday the coalition was hopeful the Assembly would reconsider its votes and override the veto. But if the law goes to a referendum, the unions are "OK with that decision," he said.

"It doesn't hurt us," he said. "(But) we're disappointed that the Assembly didn't seize upon an opportunity to move forward."

If voters end up repealing the law, city code prevents the Assembly from re-enacting the measure for two years.