PHOENIX—As the academic year winds down, Creighton School Principal Rosemary Agneessens faces a wrenching decision: what to do with veteran teachers whom the state education department says don't speak English well enough.

The Arizona Department of Education recently began telling school districts that teachers whose spoken English it deems to be heavily accented or ungrammatical must be removed from classes for students still learning English.

State education officials say the move is intended to ensure that students with limited English have teachers who speak the language flawlessly. But some school principals and administrators say the department is imposing arbitrary fluency standards that could undermine students by thinning the ranks of experienced educators.

The teacher controversy comes amid an increasingly tense debate over immigration. Arizona Gov. Jan Brewer this month signed the nation's toughest law to crack down on illegal immigrants. Critics charge that the broader political climate has emboldened state education officials to target immigrant teachers at a time when a budget crisis has forced layoffs.

"This is just one more indication of the incredible anti-immigrant sentiment in the state," said Bruce Merrill, a professor emeritus at Arizona State University who conducts public-opinion research.