My neighbor's trashcan blocks my mailbox, can I move it legally?

On my block all of our house have our mailboxes on one side of the street so I have to cross the street to get to my mailbox. All of the mailboxes come in pairs sharing one pole for each pair. I share my mailbox pole with my neighbor directly across the street from me. A month ago some people bought that house and every week when they set out their trash they set it directly in front of our mailbox. Because of this when the mailman does his route he skips our box and we get a note the following day saying something like "Could not delivery mail on Tuesday, please keep your mailbox free from obstruction." Can I move my neighbors trash cans away from our mailbox just before mail is delivered or would I be breaking the law for messing with other people's property? A side note, talking to the new neighbors has not done any good. I've asked them several times not to do this and they continue doing it anyway.