14.06 All clubs in the competition must make at least 5% of the total capacity of their stadium available exclusively to visiting supporters, in a segregated, safe area. In addition, visiting clubs are entitled to purchase up to 200 top-category tickets (unless otherwise agreed between the two clubs in question) for their VIP supporters, sponsors, etc. (see Articles 16 and 23 of the UEFA Stadium Infrastructure Regulations and Article 19 of the UEFA Safety and Security Regulations).
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I believe that Barcelona challenged this in court on the basis that they would have to evict season ticket holders from their seats and won. I heard that a long time ago though.
5%.
From the UEFA CL regs:-
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Ticket allocations
14.06 All clubs in the competition must make at least 5% of the total capacity of their stadium available exclusively to visiting supporters, in a segregated, safe area. In addition, visiting clubs are entitled to purchase up to 200 top-category tickets (unless otherwise agreed between the two clubs in question) for their VIP supporters, sponsors, etc. (see Articles 16 and 23 of the UEFA Stadium Infrastructure Regulations and Article 19 of the UEFA Safety and Security Regulations).
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