A group of 20 consumer organizations on Wednesday evening said it's sending a letter to antitrust regulators around the world, highlighting concerns over Google's proposed acquisition of the fitness tracker pioneer Fitbit. 

Google last year announced the $2.1 billion deal with Fitbit as an attempt to bolster its business in wearable technology, like smartwatches and other devices.

The letter is being sent to authorities in seven different jurisdictions: the US, UK, European Union, Canada, Australia, Mexico and Brazil. In the US, it's going to the Department of Justice and Federal Trade Commission. In the EU, the letter is being sent to the office of competition commission Margrethe Vestager. EU regulators have until July 20 to decide whether to clear the acquisition. 

The group behind the letter consists of NGOs and other organizations in several regions. They include the Open Markets Institute, Omidyar Network and Center for Digital Democracy in the US; the Open Society European Policy Institute and Access Now in the EU; and Red en Defensa de los Derechos Digitales in Mexico.

The letter calls Google's buyout of Fitbit a "test case" for big tech acquisitions, as Silicon Valley companies expand in part by obtaining data from competitors.  

"Google could exploit Fitbit's exceptionally valuable health and location datasets, and data collection capabilities, to strengthen its already dominant position in digital markets such as online advertising," the letter reads. "Google could also use Fitbit's data to establish a commanding position in digital and related health markets, depriving competitors of the ability to compete effectively. This would reduce consumer welfare (including degrading data privacy options), limit innovation and raise prices."

A Google spokeswoman on Wednesday denied that the acquisition is about collecting the data of a competitor, insisting the goal of the buyout is to build up the company's hardware efforts. 

"This deal is about devices, not data," the spokeswoman said. "The wearables space is highly crowded, and we believe the combination of Google and Fitbit's hardware efforts will increase competition in the sector, benefiting consumers and making the next generation of devices better and more affordable."

The letter comes as Google already faces intense scrutiny over its competition practices. The search giant is under investigation by the Justice Department, as well as a coalition of state attorneys general probing the company's dominance in online advertising. The Justice Department is reportedly expected to file a case this summer.