Citi and Barclays share the right to issue co-branded cards for American Airlines in the USA, and now Wells Fargo is issuing a card which allows the cardholder to earn AAdvantage miles. Citi and Barclays may see this as diminishing the value of their relationship with AA. I imagine that if Bilt is seen as a "rent rewards" program, which happens to have its own co-branded credit card, this is not a breach of contract, but Citi and Barclays may nonetheless see it as a problem because Wells Fargo has a massive retail presence.