(CNN) -- The Chicago Board of Education voted Wednesday to close 50 schools, a controversial move that drew sharp criticism from the city's teachers union.

The vote comes two months after officials announced plans to shutter the schools.

The closures "will consolidate underutilized schools and programs to provide students with the quality, 21st century education they need to succeed in the classroom," Chicago Public Schools said in a statement Wednesday.

The Chicago Teachers Union opposed the closures, which it said would disproportionately affect African-American students.

"Today is a day of mourning for the children of Chicago. Their education has been hijacked by an unrepresentative, unelected corporate school board, acting at the behest of a mayor who has no vision for improving the education of our children," said Karen Lewis, the union's president. "Closing schools is not an education plan. It is a scorched earth policy."

In a written statement, Lewis said district officials had manufactured "the underutilization crisis," and that shuttering the schools will not save a significant amount of money.

The union also had warned that the move would expose students to gang violence and turf wars, an apparent reference to neighborhood loyalties.

The union went on strike last year. The city's nearly 30,000 teachers walked out on September 10, objecting to a longer school day, evaluations tied to student performance and job losses from school closings.

With school districts across the country dealing with financial shortfalls and pressures to make reforms, the strike quickly gained national attention. It pitted the teachers union against Chicago Mayor Rahm Emanuel, who spoke in support of the school closings in March.

"This decision has been delayed for a decade, and it's our children and our city that have paid the price for inaction," he said. "Consolidating schools is the best way to make sure all of our city's students get the resources they need to succeed in the classroom."

CPS currently has 403,000 students, with seats for more than 511,000, and close to 140 of its 681 schools are more than half empty, according to the district.

CNN's Cristy Lenz, Kara Devli, Dana Ford and Katherine Wojtecki contributed to this report.