Minicab operator Uber's tax affairs have been referred to HMRC by London's taxi and minicab regulator Transport for London (TfL).
The move follows a complaint from senior Labour MP Margaret Hodge that Uber was "opting out of the UK tax regime".
London mayor and TfL chair Boris Johnson said TfL had no powers over where a company pays tax.
The app's Dutch operating firm, Uber BV, does not pay tax in the UK.
"TfL has raised this issue to the appropriate body, the HMRC, for them to consider," Mr Johnson wrote in a letter to Ms Hodge.
Ms Hodge said she was "pleased".
"I hope that HMRC will carry out a rigorous and thorough investigation to ensure that Uber is paying an appropriate level of tax in the UK, rather than constructing artificial structures to get out of paying its fair share," she said.