Ofcom has fined TalkTalk £750,000 for making an excessive number of abandoned and silent calls, the regulator said.
Ofcom said the telecommunications provider made 9,000 silent and abandoned calls to potential customers between February 1 and March 21, 2011 through two of its call centre operators.
The fine follows an investigation as part of Ofcom's monitoring and enforcement programme aimed at reducing harm caused by such calls.
Ofcom's investigation found that TalkTalk exceeded the limit of abandoned calls organisations can make four times in 2011 during one of its telemarketing campaigns. It also failed to ensure that information messages were played, meaning consumers received silent calls.
As a result, TalkTalk made approximately 9,000 silent and abandoned calls to consumers.
During a separate marketing campaign, TalkTalk did not adequately follow Ofcom's policy by failing to make a "reasoned estimate" of the accuracy of its answer machine detection (AMD) technology and also failed to keep adequate records to demonstrate compliance.
On one day in the same period, TalkTalk failed to keep to a policy that a call centre agent is guaranteed to handle a call if a previous call to the same number that day was picked up by an answer machine.
Ofcom said TalkTalk was ultimately responsible for the actions of the two call centre operators associated with the breach, Teleperformance Limited and McAlpine Marketing Limited.
Ofcom's consumer group director, Claudio Pollack, said: "Silent and abandoned calls can cause annoyance and distress to consumers. Companies must abide by the law and Ofcom's policies. If they fail to do so then Ofcom will take firm action.
"Today's penalty sends out a strong message to organisations using call centres that they must comply or face the consequences."
A TalkTalk spokesman said: "In February and March 2011, two of TalkTalk's suppliers, Teleperformance and McAlpine Marketing, made a number of silent and abandoned marketing calls.
"TalkTalk demands high standards from the companies it works with and as a result TalkTalk immediately stopped using these suppliers. Both suppliers addressed the root cause of the problem and TalkTalk will fully recover the financial penalty imposed by Ofcom from these companies.
"TalkTalk works with all its partners to ensure that regulations are adhered to and that customers continue to get good service and best value."