Eintracht Frankfurt stretched their unbeaten Bundelsiga streak to 10 games and broke into the top four following a 2-0 win over Cologne.
American teenager Matthew Hoppe scored for the third consecutive Bundesliga game but couldn't prevent Schalke 04 from slumping to FC Cologne.
"We will not start chasing our players and ask them whether their wives are barbers," a Union Berlin spokesperson said.
The German Hairdresser Association has asked the German Football Association (DFB) why footballers have taken to the pitch with fresh haircuts.
RB Leipzig missed the chance to go top of the Bundesliga as they were held to a 0-0 draw at home by Cologne on Saturday.
VfL Wolfsburg twice fought back from a goal down to earn a 2-2 draw against FC Cologne at the Rhein Energie stadium on Saturday.
Borussia Dortmund suffered a shock 2-1 loss to visitors Cologne on Saturday to drop four points off the pace in the Bundesliga title race.
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