The chief executive of the government-controlled body overseeing the $16.8 billion WestConnex motorway project is set to be forced to front an inquiry into Sydney's toll roads after pulling out of his scheduled appearance last week.

Dennis Cliche, the boss of Sydney Motorway Corporation, excused himself from appearing at the first day of hearings on Tuesday on the basis that it was a private company and not responsible for setting policy on road tolls.

But Fairfax Media understands the committee will formally ask for Mr Cliche to attend a hearing next month. The committee has the power to compel him to front the inquiry if he declines again.

The inquiry remains one of the few avenues available to scrutinise Sydney Motorway Corporation because, unlike government departments and agencies, it is not subject to freedom-of-information requests or budget estimates.