The Liberal Democrats have been ordered to stop making unsolicited automated calls to voters or face prosecution after being found to have breached privacy rules.
An enforcement notice has been issued by the Information Commissioner's Office (ICO) under the Privacy and Electronic Communications Regulations.
It follows the party's use of 250,000 such calls, featuring a recorded message from party leader Nick Clegg, in the wake of his conference speech last week.
The ICO ruled that the calls constituted "direct marketing" which is not allowed to be targeted at anyone who has not given prior consent.
It said "a number" of complaints had been received.