Section 5. Further relief based on a declaratory judgment or decree may be granted whenever necessary or proper. The application therefor shall be by petition to a court having jurisdiction to grant the relief. If the application be deemed sufficient the court shall, on reasonable notice, require any adverse party whose rights have been adjudicated by the declaratory judgment or decree to show cause why further relief should not be granted forthwith.

In addition to the foregoing when a decree has already been entered declaring an administrative practice or procedure as defined in section two to be illegal, and a person not a party to the original action involving said practice or procedure is adversely affected by the same or similar practice or procedure by the same agency, said person may seek relief under this chapter by filing a petition for contempt against the agency or agent continuing said practice or procedure after the entry of said decree.