Parliament is investigating whether MPs and their staff are in "contempt of the Senate" after shares in buy-now pay-later companies including Afterpay plunged following the internal circulation of a draft report.

The draft findings of an inquiry into the sector, which could recommend tougher credit regulations on the booming industry, were shared among six committee members at 7.30pm on Tuesday.

As many as 58 staff in senators' offices could also have accessed the report, which is due to be released on Friday.

The Senate will investigate whether a market sensitive report was leaked. Credit:Daniel Munoz

Shares in the providers fell an hour after the market opened on Wednesday, with Afterpay falling by 11 per cent between 11.16am and 11.37am.