Liverpool's stuttering start to the season continued with their 3-0 defeat by Manchester City on Sunday.
The Premier League champions were well beaten at the Etihad as they suffered their seventh loss in 10 matches in all competitions.
It saw Liverpool slip to eighth in the table heading into the November international break, eight points behind leaders Arsenal.
Liverpool 'do not accept' reason why goal was disallowed
The Reds' frustrations were compounded when Virgil van Dijk's 38th-minute header, which would have made it 1-1, was ruled out because team-mate Andy Robertson was standing in an offside position.
Referee Chris Kavanagh and the Video Assistant Referee agreed with the linesman's decision to flag for offside because Robertson was stood in the eyeline of City goalkeeper Gianluigi Donnarumma and deemed to have interfered with play by ducking under the ball as it flew into the net.
Within minutes of the incident, the Premier League Match Centre explained why the goal was ruled out. A statement read: "The referee’s call of offside and no goal to Liverpool was checked and confirmed by VAR – with Robertson in an offside position and deemed to be making an obvious action directly in front of the goalkeeper."
But Reds head coach Arne Slot criticised the decision in his post-match interview, saying: "It is obvious and clear that the wrong decision has been made, at least in my opinion. He didn't interfere at all with what the goalkeeper could do."
Liverpool have now taken their complaint further and contacted Howard Webb, the head of refereeing body Professional Game Match Officials Limited, suggesting that they do not believe the criteria for the goal to be disallowed was met.
According to The Athletic, the club do not accept the decision was reached for subjective reasons, and argue that the wording of the law does not suggest the equaliser should have been ruled out.
The relevant Law 11 says a player in an offside position is only penalised on becoming active by "interfering with play by playing or touching a ball passed or touched by a team-mate or interfering with an opponent by preventing an opponent from playing or being able to play the ball by clearly obstructing the opponent's line of vision or challenging an opponent for the ball or clearly attempting to play a ball which is close when this action impacts on an opponent or making an obvious action which clearly impacts on the ability of an opponent to play the ball".
Former Manchester United defender and Sky Sports pundit Gary Neville agreed with Slot's view of the decision.
Speaking on Sunday, Neville said: "I think he (Robertson) is outside of the line of the goalkeeper and the goalkeeper gets a clear view.
"You see Robertson there, Van Dijk's got a clear view. He can see it. He's got no position that he can stop. I think he's got every right to be fuming, Arne Slot."
