The head of the city’s teachers union is latching onto a recent spate of firings at a Brooklyn charter school to push Albany to make it easier for teachers at charter schools to join the union.

After the Williamsburg Charter School fired three teachers, the president of the United Federation of Teachers, Randi Weingarten, stepped in. She fired off letters yesterday to the school’s CEO, to the city’s schools chancellor, Joel Klein, and to the state Department of Education.

In a letter to the school, Ms. Weingarten said that she was “appalled” that administrators would terminate the teachers’ contracts after they attempted to organize to seek better wages and benefits.

Run as independent schools, charters are free of many of the rules, regulations, and union contracts that govern regular public schools. In New York City, eight of the 47 charter schools operate under union contracts. That includes a school run by the UFT, which opened its own elementary charter school in September and plans to open a middle school in the fall.

An English teacher at the Williamsburg Charter School, Nichole Byrne Lau, contacted the UFT when she was fired earlier this month. A few months earlier she had circulated a copy of the city’s pay scale for teachers. While her $50,000 a year salary was on par with teachers at other public schools, several of her colleagues’ salaries were not, even though they worked longer days and a longer school year than teachers at regular public schools, Ms. Lau said.

Ms. Lau formed a loose association with the other teachers to discuss how to advocate for higher salaries and benefits like maternity leave.

“When I gave them that scale, they could not believe that they were so underpaid,” Ms. Lau said.

She took a job at the Williamsburg school after graduating from Columbia University’s Teachers College because she thought the school would be teacher-friendly.

“I thought that charters would be more student-centered with teachers running the show,” Ms. Lau said.

Ms. Lau said that when she was dismissed on June 5, the school’s CEO, Eddie Calderon-Melendez, did not give a reason but said that it did not have to do with her performance.

Two other teachers who were involved in the organizing effort were also fired.

The principal’s office yesterday referred calls to the CEO, who did not return several calls seeking comment.

In recent months, the union has tried to stop Albany from increasing the number of charter schools allowed under state law. While the state Senate voted in favor of the governor’s push to raise the number of allowed schools to 250 from 100, the Assembly left Albany for the summer without voting on the measure.

Ms. Weingarten said she wants any legislation that allows for additional charter schools to include language that protects teachers who try to organize and ensures an expedited process so that administrators cannot interfere in organizing drives or harass pro-union workers. In that process, teachers could sign cards rather than have a secret-ballot election to form a union.

The policy director for the New York Charter School Association, Peter Murphy, called the union’s efforts “counterproductive.” He said that the charter law already stipulates a complaint process for teachers and that a school can have its charter revoked for violating a teacher’s rights.

“She’s exploiting this issue to try and organize the easy way, by having it mandated,” Mr. Murphy said of Ms. Weingarten.

About 1% of the city’s public school students attend 47 charter schools in four boroughs.

“As president of the New York City teachers union, a labor leader and an educator, I am appalled by what you have done and will do everything in my power to both publicize and right this wrong,” Ms. Weingarten wrote to the head of the Williamsburg charter school.

Mr. Klein toured the school earlier this year and later, in a monthly newsletter, wrote about his visit to Ms. Lau’s class, where she was teaching a lesson about the Greek gods. Last year, 93% of biology students and 100% of math students at the school who took the Regents exam passed. The school opened two years ago as the first charter high school in the city.

“We do not support or condone any schools retaliating against teachers attempting to organize,” a spokeswoman for the city’s Department of Education, Kelly Devers, said. “We’ll be looking into the allegations.”