A labor union seeking to represent 45,000 Kaiser Permanente workers in California — including about 1,250 in Santa Rosa — filed a petition Tuesday aimed at setting up a major ballot-box showdown with a rival.

The National Union of Healthcare Workers is asking federal officials to authorize an election that it said would be the largest vote by private-sector workers since the United Auto Workers unionized Ford in 1941.

If granted by the National Labor Relations Board, the election would ask Kaiser employees statewide to chose between their current union, the Service Employees International Union-United Healthcare Workers West, and rival National Union of Healthcare Workers, formed last year by disgruntled SEIU members.

"We haven't had an election this big in decades," said Nancy Cleeland, an NLRB spokeswoman in Washington.

National Union officials expressed confidence Tuesday that they had submitted signatures from "well over" the required 30 percent of the workers to be polled, but they did not cite a specific number.

The NLRB must validate the petition and determine whether there is a "window" for such an election, the latter an issue disputed by the two unions, Cleeland said. The agency hopes to resolve those matters and schedule an election to be held within 45 days, she said.

Most of the workers who would vote are members of a Kaiser unit that includes medical assistants, respiratory therapists, housekeepers and medical records clerks.

The petition filing came less than a week after Kaiser's SEIU members ratified a new national agreement that includes 9 percent pay raises over the next 27 months.

"In this economy that's wonderful," said Judie Adams, a medical assistant at Kaiser Permanente in Napa.

Adams, a 40-year Kaiser employee, said she will stick with SEIU to make sure she gets the benefits of the new contract. The new union, she said, is "grasping at straws" by asking workers to abandon SEIU.

"I think they are putting their members at risk by doing it," she said.

Tony Benson, a National Union board member and orthopedic technologist at Kaiser Permanente Medical Center in Santa Rosa, said the new contract will remain in place regardless of the election outcome.

If the National Union wins, its members could decide to negotiate a new contract, he said.

Win or lose, Benson said the election would give Kaiser workers a choice of union representation. "It's the fair thing to do," he said. "This is America."

Cleeland said the NLRB has not determined how the Kaiser contract would apply to workers who switch to a new union.

Kaiser officials said Tuesday they were neutral in the inter-union dispute and would "honor the choice" of employees in an NLRB election.

In December, about 700 employees at Santa Rosa Memorial Hospital voted for representation by the National Union instead of the SEIU.