The governing body fined its first player over comments made on Twitter earlier this season when then-Liverpool winger Ryan Babel criticized referee Howard Webb.
The FA said in a statement Saturday that messages that are offensive, use foul language or contain threats are also likely to be considered improper and lead to sanctions.
Action, though, could also come from outside of the FA.
A "social networking clarification" reminded players that "postings could also lead to civil proceedings being brought by affected parties."
A referee whose professionalism has been questioned by a player could sue for defamation.