Labour has written to the competition regulator calling for Google’s reported acquisition of Fitbit to be halted, at least until a wider inquiry into anticompetitive practices in the technology sector is completed.

Google made an offer to purchase the fitness tracking company on Monday for an undisclosed price, according to Reuters.

Tom Watson, the shadow digital, culture, media and sport secretary, has written to the Competition and Markets Authority (CMA) to request it halt the acquisition pending a full investigation of its effect on the competitive landscape.

“I have long been concerned about the data monopolies that dominate our tech market, including Google,” Watson writes. “These companies hold and gather an unprecedented amount of data on users which is then monetised through micro-targeting and advertising to amass huge profits and power. Meanwhile, the digital giants themselves remain unaccountable, unregulated, and see themselves as above the law. They have run rings around regulation for far too long.

“This is not just a business deal, it’s a data grab – and that should worry us all. Any such proposal must be subjected to the most rigorous possible scrutiny and must be fully investigated by the CMA.”

Watson specifically singles out the fact that Fitbit stores physical health data for users, who track their activity and exercise with the company’s range of connected wearable devices, as cause for concern.

“If this acquisition were to proceed, Google could have information on how we sleep, when we move, what we eat, on our breathing and our heartbeats. This data could hardly be more sensitive, but as is Google’s business model, all this information could then be used [for] micro-targeting, advertising, and behaviour modification. The risk to consumers here is significant,” Watson writes.

The CMA has already announced one market study into whether or not Facebook and Google dominate online platforms and digital advertising. Watson argues that, at a minimum, all acquisitions such as Fitbit should be paused “until the CMA’s market study is concluded and its recommendations are implemented”.

Watson has also written to the Information Commissioner’s Office expressing concern over the data aspects of the merger, calling on Elizabeth Denham, the information commissioner, to assess whether it raises privacy concerns and feed that back to the CMA.

Google has provided a fitness tracking service, Google Fit, since 2014, but the company has never offered its own hardware to go along with it, instead relying on third-parties such as Samsung to produce Android Wear smartwatches.