Celtic's chairman, John Reid, has attacked the Scottish Football Association, claiming that the club has been discriminated against historically. He also called into question the integrity of the SFA, following its handling of the Dougie McDonald affair, and said McDonald must be removed from his position as a referee." Guardian 2010
"Celtic boss Neil Lennon tells BBC Scotland's Chris McLaughlin that the club has compiled DVD footage of some of the referee decisions during the recent Champions League tie with Juventus in Glasgow." BBC 2013
"In order to fully understand what is going on, Celtic, our supporters, Scottish clubs and the general Scottish football public need transparency in these matters, and we therefore call on the Scottish FA to allow the referee, John Beaton, to explain these decisions publicly as well as any match officials involved in other similar circumstances.
In the meantime, we have requested a meeting with Scottish FA Chief Executive, Ian Maxwell, and the Association’s Head of Refereeing." Celtic statement 4th January 2019
This as well as a documentary and harassment is the level of pressure that lot put on the referees.