What law is it against to seize the owner's key?

No right. It is the developer's obligation to deliver the house to the owner. If the owner has paid the house price, the developer must deliver the house to the owner. Property management companies deliver houses to owners to fulfill their obligations on behalf of developers, only in the name of developers, not in their own names. The property management company refuses to give the owner the house key because of the owner's refusal to sign the owners' convention or other reasons, which is to attach its relevant rights in the property management contract to the developer's obligation to deliver the house, which is not in compliance with the law.

Legal objectivity:

"Regulations on Property Management" Article 35 A property service enterprise shall provide corresponding services in accordance with the provisions of the property service contract. The realty service enterprise fails to perform the realty service contract, causing personal and property safety damage to the owner, and shall bear corresponding legal responsibilities according to law. "Property Management Regulations" Article 41 The owner shall pay the property service fee in accordance with the provisions of the property service contract. If the owner and the user of the property agree that the user of the property shall pay the property service fee, the owner shall bear joint and several liability from the agreement. Property that has been completed but has not been sold or handed over to the property buyer shall be paid by the construction unit.