A complaint was raised following the Cardiff City Stadium clash, which Palace won 3-0 to all but secure top-flight survival, that the visitors had obtained information relating to Cardiff's starting line-up.
It was claimed Palace's sporting director Iain Moody, who took up a role at Selhurst Park after being sacked by Cardiff, used his contacts to find out information relating to their starting XI – an allegation he strenuously denied.
Following an investigation into the incident, the Premier League have ruled Palace breached rule B16 regarding acting in "utmost good faith" to opposition sides.
"The Premier League board has considered a complaint from Cardiff City regarding the conduct of Crystal Palace," a statement read.
"The Board found that Crystal Palace breached Rule B.16 and has exercised its summary jurisdiction and fined the club."
Breaching rule B16 reportedly carries a maximum £25,000 penalty, however the amount Palace have been fined remains undisclosed.
Cardiff reportedly sacked the member of staff thought to have been responsible for the leak in the wake of the incident and investigated other areas of the club.
