BOSTON (AP) — Critics who say unions block education reforms and make it virtually impossible to fire bad teachers will offer 10 instructors it deems the nation's worst $10,000 to quit their careers.

The Center for Union Facts, a Washington-based nonprofit, will launch a campaign Tuesday spending $1 million on ads and a billboard in New York's Times Square. It also says it's starting a Web site with data documenting how far unions go to protect bad teachers.

It's also inviting nominations for a contest to determine the nation's worst unionized teachers. The "winners" will be offered $10,000 each if they permanently resign or retire from any career in education — if they sign a release agreeing to have their name and the reasons for their selection published by the group.

Rick Berman — the center's executive director and a former labor lawyer who has represented auto and steel workers — declined to offer specifics on his group's supporters. He said that the organization has spent about $6 million since its founding in February 2006 and that it opposes union corruption and intimidation, not unions in general, he said.

Asked to name key supporters, Berman said: "When you're revealing some of the dark side of labor unions, not a lot of people want to have their names listed as supporters. We allow people funding us to announce their support on their own if they wish."

The head of the nation's second-largest teachers union, the American Federation of Teachers, called Berman an "ethically challenged attack dog."

"Berman has a record of using hidden funders to attack groups that contribute a great deal to society," said Edward McElroy, president of the federation. "Now he is coming after teachers at a time when most Americans support education and want to make improving education a top national priority."

Reg Weaver, a spokesman for the largest teachers union, the National Education Association, said school districts' evaluation policies include strict criteria to ensure teachers face consequences for poor performance.

"This union does not support a person's incompetence. This union supports a person's right to due process," Weaver said.

The campaign targets about two dozen districts from Boston to Anchorage, Alaska. The group alleges unions back policies that protect all but the worst teachers and force school districts to pay legal fees of $100,000 or more each time they replace a teacher.

In Boston, for example, the group alleges the teachers union has embraced policies that insulate nearly all teachers from firing after they work for three years and gain tenure.

The group says only 25 Boston teachers out of more than 3,600 with tenure were fired during a five-year period ending last summer — less than two-tenths of 1 percent of tenured teachers annually. In other cases, 34 Boston teachers signed settlements agreeing to leave their jobs, the group said.

"This is unknown data sponsored by unknown funders. We're not going to dignify this with a comment," said Steve Crawford, a spokesman for the Boston Teachers Union, one of 20 that the Center for Union Facts highlights in its findings.

In Lubbock, Texas, about 1,545 teachers have "term" contracts, which the Center for Union Facts said entitle teachers "to the equivalent of criminal proceedings if the district attempts to terminate them." From 2002 through 2006, not a single term-contract teacher was fired in Lubbock, the group said.

Lubbock Educators Association President Clinton Gill said the study is an effort to privatize public schools.

"Just because you get a bad evaluation doesn't mean you have to be fired," Gill said.

Shelley Potter, president of the San Antonio Alliance of Teachers and Support Personnel, noted that Texas teachers don't have collective bargaining. The statistics are misleading, she said, because "an awful lot of teachers" resign before they are fired.

The Center for Union Facts has run media campaigns against some of the nation's biggest unions, including the Service Workers International Union, the United Food and Commercial Workers, and Unite Here, representing apparel and hospitality workers.