12 March 2017 Last updated at 12:04 GMT
The Brexit secretary was asked six times by the BBC's Andrew Marr about Philip Hammond's announcement - but said he was unable to reveal details of Cabinet discussions.
The Institute for Fiscal Studies think tank has backed the proposal, arguing the current system had needed reform. But there has been criticism from Labour and the Liberal Democrats and more than a dozen Conservative MPs.
David Davis has refused to reveal whether the chancellor warned in advance that the Budget increase in National Insurance for self-employed workers amounted to the breaking of a Tory election pledge.