According to Chapter 11 Bankruptcy, the employer must first to go to the table and attempt negotiate a contract. If it can't negotiate one, it can request that the Bankruptcy Judge reject the current one and they then can impose a contract.
I'm not sure if that's the same for Chapter 9 Bankruptcy.
Even so, the problem is Bing did not first negotiate a contract in good faith before imposing on, and besides that, as the city's Consent Agreement is only binding under state law, he is required to negotiate labor contracts with the unions.
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