Leeds United have been fined £200,000 by the English Football League for watching opponents train before matches.
A member of Leeds’ staff was found acting suspiciously outside Derby’s training ground before the fixture between the two sides on 10 January.
Boss Marcelo Bielsa said he had sent a member of staff to watch every team they have played this season train.
The EFL found Leeds breached rules over treating teams with “good faith”.
Leeds have also received a formal reprimand from the EFL, which is bringing in a rule to prohibit clubs from viewing their opposition training in the 72 hours preceding a game unless invited to do so.
The EFL said in a statement that Leeds’ conduct “fell significantly short of the standards expected” and it “must not be repeated”.
EFL chief executive Shaun Harvey added: “The sanctions imposed highlight how actions such as this cannot be condoned and act as a clear deterrent should any club seek to undertake poor conduct in the future.
“We will now look to move on from this incident and commence the discussions about introducing a specific regulation at a meeting with all clubs later this month.”
The Football Association has also issued a formal warning to Leeds, Bielsa and a club video analyst.
“The FA will take appropriate action should further evidence of this nature come to light in the future,” a spokesman said.