Referee given police escort to match
Referee John Beaton was given a police escort into Ayr United's Somerset Park after allegedly receiving threatening messages following the Old Firm derby.
Beaton was criticised after Rangers striker Alfredo Morelos was not punished for several incidents in the 1-0 win over Celtic at Ibrox last week.
Beaton refereed Ayr-Falkirk in the Scottish Championship on Saturday.
Scottish FA chief executive Ian Maxwell said "a line has been crossed" and urged "respect" for officials.
Police Scotland confirmed "a complaint has been made regarding texts and calls received by a 36-year-old man".
With police inquiries "ongoing", Maxwell said: "It is with deep dismay that, in the last 24 hours, we learned of one of our match officials having had threats made against him and his family.
"We are in close contact with those involved and with Police Scotland to ensure that they are safe and that those responsible are identified and held accountable for their actions."
Beaton was driven to the Ayr-Falkirk game by SFA head of security Peter McLaughlin and escorted into the ground by two police officers and a steward.
"This is not the first time in recent weeks that our match officials have been targeted," Maxwell said.
"Another referee was allegedly threatened and assaulted at a lower-league game prior to Christmas. These incidents are isolated, but are they are unacceptable and extremely concerning when they occur."
Match officials have been criticised by several Premiership clubs this season following high-profile incidents.
On Friday, Scottish champions Celtic said Beaton should be allowed to explain his decisions publicly, after no retrospective action was taken when the SFA reviewed incidents in which Morelos appeared to make contact off the ball with Celtic's Scott Brown, Anthony Ralston and Ryan Christie.
Celtic also want a meeting with Maxwell, and the SFA said it would be happy to meet with clubs to discuss concerns.
Maxwell said: "Our match officials make hundreds of decisions each game. They take huge pride in their work, but it is inevitable and accepted that some of their decisions will be viewed differently and debated by others.
"When differences of opinion, however, manifest as threats to our officials or their families, a line has been crossed.
"I call on everyone involved in Scottish football, from the public parks to the international stage, to respect our match officials."