Utility Workers Union of America
AFL - CIO Local 127

Bargaining a contract from start to finish can take quite a bit of time, with agreements being reached point by point until the entire new contract is in place.  Sometimes, bargaining is not wrapped up by the time the old contract has expired.  When that happens, one of two things takes place:  either the parties keep bargaining or there is a showdown then and there.  Depending on a number of legal factors and what the parties work out, if bargaining continues past the expiration date of the old contract, sometimes the terms of the old contract will remain in effect, anyway.  So even though in some ways you’re in between contracts, your employer still has to do what the old contract required.
—Adapted from The Union Member's Complete Guide, by Michael Mauer