The dispute, which is threatening to derail a police investigation, centres on hard drives and photographs seized by the force from the home of forensic computer expert Jim Bates.
The search of Bates' home was ruled to be illegal but the force is resisting a High Court order to return the material.
In the latest development the High Court has issued Avon and Somerset's chief constable Colin Port with a summons alleging contempt of court.
Children Rights Alliance of England legal director Katy Swaine said: "It is very unfortunate that a dispute appears to have arisen in this case which may be causing a delay in protecting children from harm."
She hopes the matter can be resolved adding: "It is essential the police should have access to material which may assist in their investigations of child abuse, particularly to identify abused children and enable them to be protected."
In a statement issued by Avon and Somerset Police, Colin Port said: "I can confirm that proceedings alleging I am in contempt of court have been served on behalf of Mr Bates. I am taking independent legal advice as to my position."
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Legal dispute could derail child pornography case
A legal dispute between a computer forensic expert and Avon and Somerset Police over a child pornography case has been condemned by a children's rights group.
