Schools Chancellor Joel Klein’s efforts to give principals more control over their schools provided they meet certain achievement goals was criticized yesterday by the president of the principals union, who sent a letter to her members encouraging them not to “succumb to pressure.”

The president, Jill Levy, also filed a complaint with the state Public Employment Relations Board earlier this week charging the Department of Education with unfair labor practices.

“When we decided to give more power to principals the last group expected to oppose us was the principals union,” a spokesman for the Department of Education, David Cantor, said.

Starting in September, about 150 schools will join the 48 currently in the “autonomy zone, ” a pilot group whose principals are mostly freed from many administrative constraints. Mr. Klein announced earlier this year that he was looking to add 150 more schools to the zone and would change the name to “empowerment schools.”

Principals in participating schools are given more control over hiring and spending. They are able to control the expenditure of about $250,000 that was previously controlled by the central administration or was restricted.

The deadline for applications is midnight tonight.

About 270 schools have started filling out the online application to join the empowerment zone, but Mr. Cantor said it was impossible to tally the number of completed applications.