Suzanne Tecza had spent a year redesigning the library at Middle School 126 in Williamsburg, Brooklyn, including colorful new furniture and elaborate murals of leafy trees. So when her principal decided this year to give the space to the charter high schools that share the building, Ms. Tecza was furious.

“It’s not fair to our students,” she said of the decision, which gives the charter students access to the room for most of the day. “It’s depriving them of a fully functioning library, something they deserve.”

In Red Hook, Brooklyn, teachers at Public School 15 said they avoid walking their students past rooms being used by the PAVE Academy Charter School, fearing that they will envy those students for their sparkling-clean classrooms and computers. On the Lower East Side, the Girls Preparatory Charter School was forced to turn away 50 students it had hoped to accept because it was unable to find more room in the Public School 188 building.

Mayor Michael R. Bloomberg has made charter schools one of his third-term priorities, and that means that in New York, battles and resentment over space  already a way of life  will become even more common. He and his schools chancellor, Joel I. Klein, have allowed nearly two-thirds of the city’s 99 charter schools to move into public school buildings, officials expect two dozen charter schools to open next fall, and the mayor has said he will push the Legislature to allow him to add 100 more in the next four years.