If you haven't heard, Amtrak workers were ready to go on strike on January 30th, since they have been working without a contract for several years. Thankfully, Amtrak has reached a contract deal with several of its unions, possibly stopping the first Amtrak strike from occuring. However, the union members have to vote on the new contract first to finalize everything.
If the workers were to go on strike, not only would Amtrak service be canceled, but a lot of SEPTA, Long Island Railroad, New Jersey Transit, Metro North Railroad, and other commuter rail lines would be effected as well. Many of these lines run on Amtrak's tracks, using their powersources, dispatchers, and some of their stations. Those lines probably wouldn't have been able to run at all if Amtrak workers were picketing.
More information here: http://www.philly.com/philly/wires/ap/news/state/pennsylvania/13905771.html