Liverpool have written to the PGMOL asking for clarification after they were left frustrated by two decisions they believe proved costly against Aston Villa.
There has a string of incidents in recent weeks with match officials during Liverpool games and exasperation with Anfield was increased on Saturday following incidents either side of half-time that left them perplexed.
Tyrone Mings was booked by referee John Brooks for a chest high challenge on Cody Gakpo that left the Netherlands international writhing in agony; his shirt was ripped in the collision and he was left with stud marks on his torso.