Rodriguez admitted in 2009 that he used PEDs while with Texas from 2001-03 but has repeatedly denied using them since.
His penalty was more than double the previous high for a PED suspension, a 100-game ban given last year to San Francisco pitcher Guillermo Mota for a second offense. Kansas City infielder Miguel Tejada was given a 105-game ban last summer following a third positive test for amphetamines.
Rodriguez is still signed by the Yankees through 2017 at salaries of $21 million in 2015 and $20 million in each of the final two seasons, part of his record $275 million, 10-year contract with the Yankees.
The players' union has often succeeded at persuading arbitrators to overturn or shorten drug suspensions. In the era before the drug agreement was reached in 2002, LaMarr Hoyt, Ferguson Jenkins, Pascual Perez and Willie Wilson were among those who had success in hearings. Steve Howe's lifetime ban for a seventh suspension related to drugs or alcohol was cut to 119 days.
FILE - In this Sept. 13, 2013 file photo, New York Yankees' Alex Rodriguez sits in the dugout as …
Picked first in the 1993 amateur draft, Rodriguez reached the majors at age 18 with Seattle and was an All-Star by 20. He seemed destined to become one of the greatest players in the history of the game, and appeared in line to break the career home run record — he ranks fifth with 647.
The 65-year-old Horowitz became baseball's independent arbitrator in June 2012. Shyam Das, who had held the position since 1999, was fired a month earlier by management following his decision to overturn Ryan Braun's 50-game suspension for a positive drug test. In his first decision, Horowitz upheld Mota's suspension.
The U.S. Supreme Court has set narrow grounds for judges to consider when overturning arbitrators, ruling in 1960 that "the refusal of courts to review the merits of an arbitration award is the proper approach to arbitration under collective bargaining agreements. The federal policy of settling labor disputes by arbitration would be undermined if courts had the final say on the merits of the awards."