Ian Paisley jnr is simply not prepared to give up the name of a prison officer who told him about an alleged files destruction policy, a judge has been told.
Lawyers for the North Antrim MLA also claimed it would erode the standing and rights of elected representatives if he was forced to reveal his source.
Mr Paisley's stance is being challenged by the public inquiry into the murder of LVF leader Billy Wright.
Tribunal chairman Lord MacLean is seeking an order compelling the DUP man to disclose the identity of the officer who made the claims.
Mr Justice Gillen yesterday reserved judgment in the case following a two-day hearing at the High Court in Belfast.
According to Mr Paisley the unidentified officer informed him about an alleged policy within the Northern Ireland Prison Service to destroy a large number of files as an emergency due to data protection legislation.
It was claimed that up to 5,600 documents were destroyed shortly after Wright (37) was shot dead by republicans inside the Maze Jail in December 1997.
During the case First Minister Peter Robinson went into the witness box to support his DUP colleague. He warned that society would lose out if elected representatives could not guarantee protection to those who supply them with confidential information.
Mr Paisley could be jailed if he refuses to comply with any court order to reveal the name.
But his barrister, Gerry Simpson QC, made it clear that the MLA was determined to protect the identity of his source. Mr Simpson also said the case involved a balance between the interests of justice and the public interests of politicians in this position.
He claimed the position of those elected representatives would be eroded if such an order is made.
Judgment in the application is expected to be delivered within a few weeks.