Referee Mike Dean was hit with a coin during last month's final derby at Ninian Park holding up play whilst he received treatment to the cut on his head.
It was expected that Cardiff would be hit with – at minimum – a fine for the incident following the precedent set to Newport when a linesman was hit by a coin in an FA Cup match a few years back.
But a letter sent from the FAW to Cardiff City said "After taking all matters into consideration, the FA of Wales has determined formal action against Cardiff City on this occasion would not be warranted."
Cardiff Chairman Peter Ridsdale said "We have had full and written confirmation from the FAW there will be no further action"
Cardiff have banned for life a fan who threw 'an object' during the game