The Morrison government has shut down the idea of extending its $130 billion wage subsidy to more casual workers one day after signalling it would be as "inclusive and reasonable" as possible.

Industrial Relations Minister Christian Porter said the government would "refine" the plan before it went to a vote in Parliament on Wednesday but said the essential features would not be changed.

Attorney-General and Minister for Industrial Relations Christian Porter said on Monday morning the bill would apply the definition of casual worker announced last week, requiring someone to have been "attached" to an employer for a minimum of one year. Credit:Alex Ellinghausen

Mr Porter stepped back from earlier remarks that indicated he was willing to negotiate with the Australian Council of Trade Unions on the rules for casual workers to sign up to the scheme.

The government closed off that option on Monday morning with a warning that it would not change the "essential principle" of the scheme, which is available to casual workers who have worked for one employer for the past year.