The Telegraph has been fined £30,000 over an email urging subscribers to vote Conservative on the day of the general election.
The Information Commissioner's Office has imposed the fine after the email, from editor Chris Evans, was sent to hundreds of thousands of addresses.
The ICO said: "Subscribers had signed up to receive a daily e-bulletin, but by promoting an election campaign, the paper broke the rules around direct marketing. The ICO found that none of the subscribers had given specific consent to receive that kind of marketing, a requirement under the Privacy and Electronic Communications Regulations."
ICO head of enforcement Steve Eckersley said: “People may well perceive the paper’s editorial content to have a political bias, but when The Telegraph emailed people directly, calling for them to vote for a political party, they crossed a line.”
He added: “People signed up to The Telegraph’s email service so they could catch up on the news or find out about subjects they were interested in. They did not expect to be told who they should be voting for.”
The ICO said the letter had been sent after "last-minute instruction from the editorial team", adding: "Pressure to distribute it quickly meant there was not enough time to properly consider whether the appropriate permissions were in place.
"These circumstances, along with the small number of complaints (17), were factors when deciding the fine."
Eckersley said: “Regardless of the circumstances, this organisation fell short of the law and we have acted.”
Evans' email said: "The Daily Telegraph urges its readers to vote Conservative.”
A Telegraph Media Group spokesperson said today: "Although we are disappointed with this ruling, we note the mitigating factors that the ICO highlights in its report: the response to the email was overwhelmingly positive, and the ICO agreed in its ruling that it was unlikely to cause distress.
"Indeed, only two complaints were received by the ICO. The ruling also recognises that we fully co-operated with the ICO and that we have taken steps to make sure this should not happen again."