It emerged on Tuesday that the party’s elected representatives can be fined up to £1,000 for speaking without prior permission from the DUP press office.
It was also claimed that DUP chief executive and former special advisor Timothy Johnston acts as “judge, jury and executioner” in deciding who gets punished.
Speaking to the BBC’s Nolan Show, the unidentified DUP politician said it was common occurrence for fines to be handed down to elected representatives.
“Timothy wrote to me. He emailed me and then sent me a letter saying ‘you’ve spoken to the BBC,’ which I did, ‘and we’re fining you £100,” the whistleblower said.
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Commenting on who then had the authority to issue the fine, he said: “The press office will report me to Timmy Johnston and Timmy Johnston then makes a decision whether or not to fine the person.
“The level [of Mr Johnston] is God incarnate. Timmy Johnston, you will learn as time goes by, is judge, jury, executioner, implementer, enforcer, advisor. The party view is that you have the press office decide what you think.”
He said he had never heard of a DUP councillor being fined, only MPs and MLAs, but said the process took place privately between the elected representative and Mr Johnston.
“It would never happen in public,” he added.
A party spokesman said: “The DUP operates under a constitution and a code of conduct for its members, which was passed by the central executive committee of the party.
“The chief executive, on behalf of the party officers, writes to members on code of conduct matters, as he is required to do from time to time. The party does not comment on its internal procedures.”
The spokesman added: “The party reserves the right to decide what programmes to participate in and the best mix of platforms to ensure ongoing communication with the people of Northern Ireland.”
The revelations prompted a former commissioner on public standards, Sir Alistair Graham, to say he feared the DUP’s disciplinary system “severely undermined” democracy.
“I would sincerely hope the DUP, because of the damage to their reputation this information will have made, will rethink its policy, because this is quite authoritarian and draconian, and I believe it will damage their standing,” he said.
Sir Alistair said he accepted that all political parties “are concerned to try and control the message that gets out to the public,” but added: “You are elected to represent constituents and they want to know that if they feel strongly about something, and the representative agrees with them, then they will go and talk about it and try to influence public policy on that issue, rather than follow a press line that has been determined by somebody else.”
All of Northern Ireland’s other main parties said they did not impose financial penalties on anyone who gave unauthorised media interviews.
• For more than a decade, Timothy Johnston has been a key backroom figure within the DUP.
Last year he was appointed as the party’s chief executive after a note advertising the vacancy was posted on a notice board at party headquarters.
The essential criteria for the post ruled out anyone who had not been a Stormont special advisor or very senior civil servant.
Mr Johnston has held a number of senior positions within the party, including director of policy, director of communications and has been a special advisor to all three of the DUP’s leaders – Rev Ian Paisley, Peter Robinson and Arlene Foster.
He joined the DUP in 2002 having previously been a member of the Ulster Unionist Party.
Mr Johnston grew up in a farming family just outside Portadown and is married with three children aged under eight.