Transport for NSW has announced the trial which offers free internet access to commuters, which will be provided by advertising giant APN Outdoor.

CATCH features tailored sponsored content for those wishing to avoid using their own data, though the privacy concerns lie deep within the app's terms and conditions.

Upon connecting to the Wi-Fi service, APN Outdoor will track the user's location data as well as other non-specified private information, which can be shared with third parties.

The possible collected data stretches from the expected "name, address, date of birth, location details", to more obscure information such as "drivers licence details, photographs, video, credit card details, employer and other details."

Greens MP and spokesperson for Transport Dr Mehreen Faruqi said the government is misleading its commuters.

"The Transport Minister [Andrew Constance] is boasting this as a win for the public, but is failing to make clear how the free Wi-Fi is being paid for, burying the 'catch' in the fine print," she said.

"Not making it clear to tens of thousands of bus commuters that they'll be signing up to hand over their personal information to a private company is simply irresponsible."

The service will open on 50 of the city's buses, though the government plans to expand to 1000 buses by the end of the year.

Dr Faruqi said the government needs to ensure commuters are aware what the true cost of the 'free' service is.

"It is deeply concerning that the personal information of commuters will be harvested for targeted advertising," she said. "If the cost of installing the system is being recovered by passengers becoming advertising targets, this must be made crystal clear up front."

"As usual with this government, every promise comes with a catch - and this time it's sacrificing the privacy of passengers."