PFA chairman Clarke Carlisle says John Terry's four-match ban undermines the Football Association's strong stance on tackling racism.
Liverpool's Luis Suarez was given an eight-match ban last season for racially abusing Manchester United defender Patrice Evra.
"The Luis Suarez ban sent out a strong message that racism isn't tolerated in the game," Carlisle, 32, said.
"Diluting that with this four-match ban almost undermines the initial message."
Chelsea defender Terry was given the ban on 27 September after an independent FA regulatory commission found that his words towards QPR defender Ferdinand during a Premier League game in October last year were used as an insult.
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