The two unions seeking higher wages for Seattle child-care workers have filed a lawsuit asking a judge to separate their initiative from the preschool plan proposed by Seattle city leaders so that voters don’t have to choose between them on the November ballot.

The lawsuit, filed Wednesday in King County Superior Court, is the latest salvo in a conflict brewing for months between the unions on one side and Mayor Ed Murray and City Council President Tim Burgess on the other.

Murray and Burgess have led the city’s yearlong effort to create a narrowly tailored, high-quality preschool program for 3- and 4-year-olds.

The unions behind the other preschool measure — Initiative 107 — are the Service Employees International Union (SEIU) Local 925 and the American Federation of Teachers-Washington (AFT).

For months, they lobbied the council to include better pay and training opportunities for all child-care workers in the city’s proposal. But when the two sides couldn’t agree, the unions spearheaded a coalition called Yes for Early Success, which collected more than 30,000 signatures to put I-107 on the ballot.

The initiative would set city policy on how much parents should pay (no more than 10 percent of family income) and how much child-care workers should earn ($15 an hour), but it doesn’t specify how the city would pay for that policy.

It would also require child-care teachers and staff members to obtain training and certification through a center jointly operated by the city and a provider hired by the city.

To qualify, the provider must have existed more than five years and have successfully negotiated a contract for child-care workers that increased wages and benefits.

Last month, the City Council voted to put both proposals on the ballot, but also voted 6-to-3 to take a position against I-107.

Burgess argued that the unions’ proposal contradicts the city’s preschool plan, specifically in areas that directly affect quality, such as teacher training and credentials.

The council voted to consider I-107 as a competing, rather than complementary measure, which means voters would have to decide first whether they want a preschool program at all, and then to choose between the two options.

The lawsuit argues that voters shouldn’t have to choose because the two measures have distinct, but complementary, goals.

I-107 seeks to improve the pay and training of about 4,500 workers caring for children from birth to school age in a variety of settings.

The city’s program would focus on high-quality providers and eventually would serve 2,000 children in 100 classrooms by 2018.

A spokesman for the Seattle City Attorney’s Office said he had not seen the lawsuit yet and could not comment.

The unions also have filed an ethics complaint against the city with the state auditor, the state Public Disclosure Commission and the Seattle Ethics and Election Commission.

The complaint alleges the city improperly made policy decisions opposing I-107 behind closed doors and provided The Seattle Times editorial board with a fiscal analysis of I-107 that the city refused to provide to the coalition.

The lawsuit accused the City Council of discussing and carrying out legislative duties related to I-107 in those closed-door sessions in violation of open-meetings laws.

A hearing is scheduled Aug. 12.

John Higgins: 206-464-3145 or jhiggins@seattletimes.com On Twitter @jhigginsST