The leaders of two labor organizations representing health care professionals announced Thursday that they had approved an affiliation agreement that will bring 34,000 registered nurses into the American Federation of Teachers, the largest union of professionals in the AFL-CIO.

The National Federation of Nurses, which represents nurses across the country, will affiliate with the teachers union, whose 1.5 million members include more than 48,000 nurses and thousands of other health care professionals.

Barbara Crane, the president of the nurses federation, said her group’s national board voted to join forces with the teachers union to give the nurses more political clout and money to try to unionize more nurses.

“We were not going to be able to achieve some of our goals unless we found a partner,” said Crane, whose union represents 34,000 nurses in Montana, Ohio, Oregon and Washington. “We wanted a professional union that believes in growth through organizing.”

Competition has been growing among various labor groups wanting to expand the unionization of the nation’s 3 million nurses, including the Service Employees International Union, which represents 90,000 nurses, and National Nurses United, a union that represents only nurses, 185,000 of them.

Officials with National Nurses United asserted that it would have been smarter for the nurses federation to join an all-nurses union instead of a union dominated by teachers.

But the National Federation of Nurses decided to in effect merge with the teachers union after considering and then rejecting affiliation with the American Federation of State, County and Municipal Employees and the Office and Professional Employees International Union.

Randi Weingarten, president of the American Federation of Teachers, which has 1.3 million members, said the affiliation demonstrates her union’s ability to grow despite legislative actions that have weakened public sector unions in Wisconsin and elsewhere.

“When many people out there are trying to write our obituary, this is a pretty big inflection point — this shows the opposite,” Weingarten said. “This will make a very big difference in terms of the size of the AFT’s voice in health care.”

Her union already represents 48,000 nurses.