The Chicago Cubs sent out the following email to spring season ticket holders late Friday (and I assume similar emails were sent out by the other 29 teams):
Please be aware MLB has informed all clubs that Spring Training games will begin no earlier than March 18. Please visit www.mlb.com/update for more information.
Since you previously elected to receive a credit, we will apply the same choice for the games originally scheduled to be played at Sloan Park Sunday, March 13, Monday, March 14, and Thursday, March 17. No action is required.