Police Scotland has refused to let serving officers answer questions from the Scottish Parliament (pictured, Shutterstock) on why they unlawfully accessed telecoms record to identify journalistic sources.
The force was publicly censured by the Interception of Communications Commissioner in November after it accessed the telecoms records of four individuals to find out if they were journalistic sources.
The move followed publicity in the Sunday Mail about police failure to solve a decade-old murder case.
The force obtained the information without obtaining approval from a judge, thereby breaching a change in the law which was made in March following the Press Gazette Save Our Sources campaign.
MSPs on the Justice Committee want to hear from four officers who were connected with the decisions leading up to the breaches.
They have persisted after an earlier request was met by a letter from the force's legal services stating it was concerned the committee "may be acting beyond its powers".
In a letter to the Justice Committee turning down the request for a second time, deputy chief constable Neil Richardson said there were "critical legal issues" that had not been resolved.
He also said he was concerned about the "issue of risk" to the four officers.
MSPs agreed instead to take evidence from assistant chief constable Ruaraidh Nicolson at their meeting tomorrow.
But the committee emphasised last week that the agreement to hear Nicolson was "without prejudice to any further decisions the committee may take in relation to these matters".
In a letter to Richardson, deputy convener Elaine Murray said: "The committee will consider next steps, including whether to call further witnesses, in the light of evidence taken next Tuesday."
In November, Sir Stanley Burton, the Interception of Communications Commissioner, said Police Scotland had contravened the Regulation of Investigatory Powers Act Code of Practice on five occasions, all linked to the investigation into the murder of prostitute Emma Caldwell.
At an earlier hearing of the committee, Richardson said the breaches had been a ''mistake'' he blamed on one officer's ''misinterpretation'' of new guidelines, the speed of their introduction and insufficient training.