The Bayern Munich head coach raced to confront the assistant referee during the 1-1 draw with Schalke after Robert Lewandowski saw a goal disallowed.
Guardiola was angered at the decision, although his frustration soon passed when Arjen Robben netted the opening goal for Bayern, causing the 44-year-old to embrace the fourth official back in his technical area.
Although he dismissed the incident after the game, Fandel has hit out at the Catalan and warned him to not repeat the act.
"Pep Guardiola would do well to adjust his attitude," Fandel told Sportbild.
"With all due respect to strong emotional reactions, we crossed a line. A coach leaving his technical area to rush towards an assistant at the corner flag needs to be sent to the stands.
"The fact that he got away with a warning against Schalke should remain an isolated case.
"You cannot touch the body of a referee. Pep Guardiola should change his behaviour immediately."
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