The FBI is investigating whether a section of commuter train tracks was sabotaged after Metra workers discovered a dozen railroad spikes missing in an area on Chicago's South Side.

The spikes hold down metal plates that bind the rails to wooden ties.

"If a sufficient number of spikes are removed in a contained location, there's the potential for the rail to shift, which would lead to disastrous results and train derailment," said Federal Railroad Administration spokesman Steve Kulm.

Metra employees discovered the missing spikes Monday and notified police and federal authorities, including the Department of Homeland Security and the Transportation Security Administration, which investigates threats to planes and trains.

The FBI said it was conducting a criminal investigation into "sabotage." FBI spokesman Ross Rice said agents were checking for possible connections to a domestic violence case involving a Metra engineer.

"No one has claimed responsibility or called in a threat," Rice said. "No similar incident has been reported to us in the metropolitan area. This is a serious incident, and we are aggressively investigating."

Gunshots were fired at two Metra trains on the same line in June, about two miles south of where the spikes were removed.

Metra officials were concerned the target of the shots may have been the engineer involved in the domestic case, who allegedly was being harassed by her estranged husband, said agency spokeswoman Judy Pardonnet. The woman wasn't operating trains on the days of the shooting.

The affected tracks carry three commuter lines, including the Metra Electric Line to University Park and Blue Island, and the South Shore Line to Michigan City and South Bend, Ind.