London (AP) — Officials say that an advertising firm must immediately stop using its network of high-tech trash cans to track people walking through London’s financial district.

The City of London Corporation says it has demanded Renew pull the plug on the program, which measures the Wi-Fi signals emitted by smartphones to follow commuters as they pass the garbage cans.

In one interview, Renew chief executive Kaveh Memari said he would sell the data to “anyone.”

The company tested the technology in May but received a burst of publicity last week, with some wondering whether the technology was legal.

The City of London Corporation is responsible for the city’s historic “square mile,” home to financial institutions, law firms and tourist landmarks.

Renew did not immediately return a call seeking comment Monday.