The Labour MP David Lammy has been fined £5,000 by the Information Commissioner for instigating 35,629 nuisance calls over two days urging people to back his campaign to be London Mayor.
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 individuals.
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.
Mr Lammy's mayoral campaign ultimately ended in failure. He finished fourth, picking up fewer than 10 per cent of votes.
The nomination was won by Sadiq Khan - the favourite to beat Conservative candidate Zac Goldsmith in the election on May 5.
Additional reporting by PA
