Getting your Trinity Audio player ready...

The Brotherhood of Locomotive Engineers went on strike against the Union Pacific Railroad late Friday, halting freight trains on 39,000 miles of Union Pacific tracks and temporarily halting commuter rail service to Chicago’s north, northwest and west suburbs.

The strike surprised the railroad, Metra and Chicago-area commuters who expected to ride home on Metra trains departing the Ogilvie Transportation Center after 11 p.m. Friday.

Instead of boarding their trains, the commuters were turned away by railroad employees and were left to angrily work cell phones in search of alternate ways to get home or find places to spend the night.

However, the union apparently did not intend to strike Metra trains. Crews were assembled to operate the day’s last trains out of the station leaving around 12:30 a.m. Saturday on Metra’s Union Pacific North line to Kenosha, Northwest line to Crystal Lake and the West line to West Chicago.

A statement posted by the union on its Web site (www.ble.org) said the strike was provoked by the railroad’s imposition of new rules for allocation of personal leave days for locomotive engineers. Mark Davis, a spokesman for the Union Pacific, said the railroad was preparing to go to court to stop the strike, which he called illegal.

“There are certain procedures that must be followed by management and labor” before the union may call a strike, and those procedures were not followed in this case, he said.

John Bently Jr., a union spokesman based in Cleveland, said late Friday that union members had been instructed to operate the last Metra trains scheduled to depart from the downtown Chicago commuter rail station. He said he didn’t know why union members had declined to operate the first trains departing after 11 p.m.

He said union members expect to continue operating Metra trains in coming days regardless of the strike’s status against the Union Pacific freight operation.