Service was disrupted on the two main commuter train lines leading into Milan, ANSA reported.
Two train runs were canceled and 12 others had delays of up to 50 minutes.
The country has had a string of recent copper thefts, the report said.
Four men, aged 18 to 21, were arrested Tuesday in Milan for allegedly stealing copper drainpipe from a building site.
They men allegedly told police they were forced to steal the pipe because they were unemployed and threatened by economic difficulties, ANSA said.