The Information Commissioner's Office (ICO) is investigating the personal data practices of four of the UK's biggest online dating companies.
The investigation follows a recent survey by the ICO of major UK dating websites, which identified areas where the Data Protection Act was not being followed.
The ICO has now written to eHarmony, match.com, Cupid and Global Personals, as well as industry trade body the Association of British Introduction Agencies.
The ICO has outlined the main areas of concern that the survey found and the companies are being asked to respond with how they are addressing those concerns.
Areas which the ICO is concerned about include poor visibility of the terms and conditions that give the website consent to use personal information in certain ways, and those terms and conditions making reference to the dating company having "perpetual" or "irrevocable" licence to use members' data.
It is also concerned about websites claiming to take no responsibility for the loss of or damage to personal information, and users being expected to provide personal details before terms and conditions are provided.
The ICO letters came as the BBC's Panorama programme investigated the "scale of apparent unscrupulous practices being employed by some dating websites", said the ICO.
Simon Entwisle, ICO director of operations, said: "The evidence we're being presented with by the media suggests quite concerning business practices by some dating websites, and there are particular questions around how people's information is being used that need to be answered."
Entwisle said, "While media reports are painting a disturbing picture, the number of complaints we're getting from the public is not very high. That could be because this is only an issue with a small minority of websites, or it could be because people are reluctant to come forward.
"The work we're doing now will help us better understand the scale of the issue."
The ICO has encouraged users of dating websites to come forward if they have concerns about the way their data is being used.