Performance-enhancing drugs were not prohibited in baseball prior to the 2002 Joint Drug Program. Fay Vincent’s 1991 memo and other commissioner proclamations were no more binding than a bill that is passed by Congress, but vetoed by the President. Arbitrators would not uphold the memo as the law of baseball. It was not until 2002 that the players and owners agreed to a testing and enforcement program. A second positive test was a punishable offense in 2004, but there was no sanction for first-time offenses until 2005.
If drug testing only required an act of the Commissioner, then there would have been no need for contentious negotiations with the MLBPA.