The police and the National Fraud Intelligence Bureau have written to two sites known to share links to pirated copies of music, movies and games.
The letters warn the operators of the sites they are breaking UK laws that carry heavy jail sentences. If site owners do not contact police by 14 June they face further action, the letters say.
In a statement, the City of London Police, said: "These websites are able to operate and profit from advertising on their sites without having licenses or paying the creators and owners of the films, TV programmes, music and publications.
"Intellectual property crime is a serious offence that is costing the UK economy hundreds of millions of pounds each year."
In addition, said the statement, the action would help protect UK citizens from the malicious software and other harmful programs that could be found on these sites.
The initiative came out of work done with UK advertisers, the Federation Against Copyright Theft, the British Phonographic Industry (BPI) and the Publishers Association.
Source: BBC News
