The competition regulator is pressing ahead with preparations for a controversial new inquiry into the banking sector despite internal concerns about the probe and a lack of formal approval from Treasurer Josh Frydenberg.

Agenda items for a meeting of the Australian Competition and Consumer Commission's Financial Services Board on Friday, obtained by The Sydney Morning Herald and The Age, outline the regulator's plans for the inquiry, which has upset the banking sector.

Some say Rod Sims needs a smoking gun in the TPG case. Credit:AFR

Documents obtained by the Herald and The Age show the regulator was concerned about proceeding too far on the inquiry without political support. "There may be a perception that we are commencing the inquiry before the Treasurer has formed a view on whether it should proceed," the documents read.

Board minutes for the September meeting and agenda items for Friday's meeting reveal the ACCC's vision for the inquiry would include meetings with new financial digital upstarts such as Afterpay and neobank Xinja.