A Labour MP has apologised "unreservedly" after being fined up to £5,000 for making 35,000 nuisance calls during an abortive bid to become the party's London mayoral candidate.
The calls, which played a recorded message urging people to back David Lammy's campaign, were placed over just two days last August.
Information Commissioner Christopher Graham found Mr Lammy broke privacy rules because he did not have permission to contact the Labour members using automated messages.
Mr Graham said: "The rules apply to political groups canvassing for votes in the same way they apply to salespeople offering a discount on double glazing. If you want to call someone in this way, you must follow these rules. Mr Lammy did not, and that is why he has been fined.
"It's not good enough to assume the people you're contacting probably won't mind. The law requires you to have permission before making calls with recorded messages. And if the law isn't followed, the regulator will act."
If Mr Lammy pays by April 5 the fine will be reduced to £4,000.
The Tottenham MP came fourth in the Labour Party's selection contest last summer, securing 9.4% of first preference votes. Sadiq Khan was the eventual winner.
Labour provided Mr Lammy with contact details of members, but his team "did not make the additional checks necessary to ensure he was able to contact the people with recorded messages".
Mr Graham said there had only been one complaint about the breach of the Privacy and Electronic Communication Regulations, and the calls were "unlikely to have caused distress".
"The commissioner has considered the likely impact of a monetary penalty on Mr Lammy," the report said.
"The Commissioner does not consider that the proposed monetary penalty would cause undue financial hardship."
Mr Lammy said: "I fully accept the Information Commissioner's decision and apologise unreservedly to any Labour Party member or registered supporter that felt upset at receiving an automated call from my campaign.
"If I had known that additional permission was required to make automated calls then I would have sought it before any calls were made."