A Bundesliga match between Union Berlin and Wolfsburg was stopped twice due to fan protests against Hoffenheim owner Dietmar Hopp on Sunday.

The match official halted the game after 33 minutes and once more just before half time when Union supporters unfurled banners and sang chants about Hopp.

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It is the second time in as many days that referees have delayed play in the Bundesliga with Bayern Munich and Borussia Dortmund fans also involved in protests in their two respective games on Saturday.

After Bayern's 6-0 win over Hoffenheim, CEO Karl-Heinz Rummenigge told reporters: "I am deeply ashamed for the behaviour of these people. That is inexcusable. It is the ugly face of football.

"I have apologised to Dietmar Hopp. We have filmed everything and these people will be held accountable."

Union held a 1-0 lead but the referee Bastian Dankert led both sets of players into the dressing room amid the continued protests. The club's stadium announcer Christian Arbeit told the fans the game was close to being called off. The match finished in a 2-2 draw.

The first interruption led to an announcement from the PA as the official acted in line with the three-step protocol against racism, which late last week was expanded by the German Football Association to act against protests and hate banners.

During the break, Union sporting director Oliver Ruhnert said: "How should we prevent this from happening? The first banner shown by the fans addressed legit questions and you have to be prepared to accept criticism.

"I would have wished for no intervention. The only critical thing was that it was against the DFB. But you'd have to interrupt every match in the future. I regard that as very critical."

There were several matches in the German third tier on Sunday which were also stopped due to anti-Hopp protests.

Hopp has been a lightning rod, especially in recent weeks, for some German fans who oppose the way he used his wealth to help Hoffenheim climb through the lower leagues to the Bundesliga with consecutive promotions more than a decade ago.

Dortmund supporters were recently handed a two-year ban from travelling to Hoffenheim following anti-Hopp protests.

Fans protested against that ban last week with the game between Borussia Monchengladbach and Hoffenheim stopped as a result. That happened on the same day that games paid tribute to 10 people killed in a racially-motivated shooting in Hanau, and the German FA announced they had launched an investigation into the incident.

Later on Sunday, Schalke, who are Hoffenheim's next opponents, released a statement warning their supporters they will not tolerate "hate, violence and defamation."

They added: "We clearly distance ourselves from such banners, defamations and personal insults and do not accept any trivialisation. We will punish such behaviour according to our stadium rules and exclude those responsible.

"Should such incidents become visible in Tuesday's cup match against Bayern Munich, in our match against Hoffenheim next weekend or at any future matches at the Veltins Arena, our team will leave the pitch, regardless of the time of play, the result or possible consequences."

Schalke also said they would "continue our talks with all fan groups with the clear goal and expectation that they won't tolerate such misconduct, let alone support it."

ESPN's Germany reporter Stephan Uersfeld also contributed to this report.