Conservative London Assembly member Andrew Boff said it still wasn't clear where the cash was coming from and who's paying for the transformation of the stadium.
Andrew Boff added: "We still don't really know, but chances are we're all contributing. Taxpayers shouldn't be paying for Premiership football clubs.
"The £154 million has to come from an already stretched LLDC budget and the knock-on effect is that the rest of the transformation of the park - the really important stuff such as housing - will suffer as a result.
"Only by ditching the requirement for the athletics track, are we likely to see more bids from the private sector, for a proper football stadium rather than the hybrid fudge we currently have."
- The site in Stratford is due to host five matches during the Rugby World Cup in 2015
- The stadium will be the permanent home of West Ham Football Club from 2016
- During construction Balfour Beatty expects to employ up to 400 people, and hire local people where possible
Balfour Beatty has won a contract worth £154 million to transform the Olympic Stadium in east London.
Last summer, Balfour was awarded the contract to convert the stadium roof and will now lead the remainder of the transformation work.