A major employer group has attacked the union "myth" of increasing job insecurity and casualisation in the Australian workforce.

New Australian Industry Group research shows casual work has hovered between 19 and 21 per cent of the total workforce during the past two decades.

The Australia Council of Trade Unions' is in the midst of its Change The Rules campaign which calls for greater job security for workers.

The ACTU is calling for a clear definition of casual work which it believes should be limited, while arguing workers in the gig economy need more rights.

"Despite the clear weight of evidence to the contrary, the ACTU seems determined to maintain that job insecurity and casualisation of work in Australia is increasing. Neither is true," Ai Group chief executive Innes Willox said.

He said the share of casual workers in Australia today was about the same as 1998.

"The proportion of people expecting to be in their current job in one year's time has been unchanged for a similar period pointing to no change in job insecurity," Mr Willox said.

He said the ACTU had started to include part-time employees in their figures about insecure work and was intent on demonising casual employment, because relatively few were union members.

"This is nonsense when, of course, the vast majority of part-time workers do not want to work full-time," he said.

Mr Willox said part-time work allowed women, older workers and students to participate in the workforce.

Last week, the ACTU pointed to jobs figures which showed less than half of all working Australians were in full-time work with leave benefits.

"The Turnbull government isn't even talking about the crisis in insecure work which has come about on its watch," ACTU secretary Sally McManus said.

"It is completely out of touch with Australian workers who are finding it harder than ever to find good, steady jobs."