Child care providers who oppose a unionization movement aimed at their businesses are headed back to court.

A group of providers, some of whom successfully sued to block a unionization effort last year, filed suit in federal court Wednesday. They seek an injunction blocking a union election authorized by a bill passed by the DFL-controlled Legislature and signed into law last week by DFL Gov. Mark Dayton.

Their attorney, Doug Seaton, argued throughout the hearings on the bill that federal labor law preempts state law in this area. He makes the same argument in the suit -- that family child care providers are "subject to the National Labor Relation Act," which prohibits "employers and independent contractors" from voting in union elections.

"By providing for an election of family child care providers, who are properly defined as employers," the lawsuit argues, the new law "is in direct conflict with the National Labor Relations Act and the Taft-Hartley Act."

Two of the plaintiffs, child care providers Hollee Saville of St. Michael and Becky Swanson of Lakeville, have long been active in fighting the unionization effort.

"If the unions have their way, we will all look like carbon copies," Swanson said.

The lawsuit only applies to child care providers, but the law also allows some personal care attendants to vote on unionization.

Jennifer Munt, spokesperson for AFSCME Council 5, which is organizing the child care workers, said the law merely gives providers the right to vote on unionization.

"There is nothing more constitutional than the democratic right to vote," she said.

She said a union could increase state subsidies for low-income children, improve training and possibly even discuss health insurance coverage for providers. The union believes it will not have a problem meeting the requirements for an election -- signed authorization cards from 30 percent of the roughly 12,700 eligible providers.

Opponents are concerned that many providers who would be affected by unionization will not be allowed to vote. The 12,700 includes licensed and unlicensed providers who care for children under the state subsidy programs. That leaves out 5-6,000 licensed family child care providers who do not currently have subsidized children in their programs, opponents say.

The suit says by excluding these providers from the vote, but subjecting them to "whatever determinations are negotiated" by the union and the state, the law violates the equal protection clauses of the state and federal constitutions.

Among the named defendants are Gov. Mark Dayton, the Bureau of Mediation Services and the Department of Human Services.

Rep. Michael Nelson, DFL-Brooklyn Park, House sponsor of the bill, said in a statement that last year's lawsuit paved the way for this year's law.

"Last year's court ruling made it crystal clear that the legislature had the authority to pass legislation allowing child care workers to have the opportunity to vote on whether or not they wish to form a union," his statement read. "No one is forcing anyone to join a union."

He called the lawsuit "frivolous" and said he is "confident it will be dismissed and child care providers will retain their ability to decide on this issue for themselves."