Is it legal to sign a maintenance company without authorization?

Illegal. According to relevant information, the contract between the property management company and the maintenance company belongs to the property disposal behavior, and can only be signed with the authorization of the owners' assembly or owners' committee. If the property company signs a maintenance company contract without authorization, then its behavior will be regarded as illegal. Article 31 of the Property Management Regulations stipulates that property service enterprises shall abide by laws, regulations and contracts, exercise their rights and perform their obligations according to law, and shall not violate the contract and damage the legitimate rights and interests of owners.