The Beverly Hills Unified School District filed a lawsuit on Wednesday asking a judge to overturn the county transportation agency’s approval of a plan to dig a subway tunnel under Beverly Hills High School.

The long-expected move is the latest escalation of a years-long battle between the district and the L.A. County Metropolitan Transportation Authority over the route of the Purple Line, which is being extended into the Westside.

The two public agencies and their supporters have presented dueling experts, reports and viral web videos on the hazards and benefits of tunneling under the high school to a proposed station in the heart of Century City.

Beverly Hills leaders prefer a Century City station near the district’s northern boundary that does not require tunneling under the high school, which they claim might endanger students and possibly hamper school expansion plans. However, the agency contends tunneling presents no danger and will allow the construction of a station that will be used by more riders.

The school district’s lawsuit seeks to set aside the Metro board’s decision this month to approve an environmental study of Purple Line’s extension from its terminus at Western Avenue. It claims the board violated California Environmental Quality Act by not making an informed decision.

Metro spokesman Dave Sotero said the agency has not been served with papers and does not comment on litigation.