Dortmund police have warned Celtic fans they will be thrown out of the stadium if they are found with pyros in this week's Champions League tie.
Celtic have an official allocation of 3,800 at the second game of the tournament although they are expected to have many more supporters travelling to Germany.
And Dormund's police department has written an open letter to the Celtic fans arriving in Germany warning about the consequences of taking pyros to the game.
They stated: "The police department of Dortmund warmly welcomes the fans of Celtic Glasgow.
"We are aware that supporting the team is an important part of the match.
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"Nevertheless, we would like to inform you that carrying and burning of flares, smoke bombs, sparklers, fireworks or any other non-approved pyrotechnics is prohibited inside the stadium as well as in public areas.
"Any violation will lead to legal consequences and will be punished.
"The police of Dortmund will not condone misbehaviour of any kind and will probably exclude those supporters from the match.
"This means that because of your misconduct and despite being here to support your team, you will not have access to the stadium."Therefore please do not use any kind of fireworks or pyrotechnics at any time during your stay in Dortmund.
"You endanger yourself and others."
