Scrapping union watchdogs could save $150m

Labor's plan to immediately abolish so-called "union busting" government agencies is forecast to save taxpayers more than $150 million over four years.

The opposition's pre-election costings show scrapping the Australian Building and Construction Commission and Registered Organisations Commission would save the budget $31 million in the 2019/20 financial year.

The coalition has fiercely defended both organisations since establishing them, arguing they guard against union misconduct and lawlessness in the construction industry.

Prime Minister Scott Morrison warned earlier in the week that winding up the ABCC would allow militant unions to control work sites across the nation.

Labor's costings show - after the first-year saving - $40 million in the two years following and $41 million in the final year of a four-year budget cycle.

The Construction Forestry Maritime Mining and Energy Union has accused the ABCC of being more concerned with "union busting" than safety.

But the commission argues it is an effective watchdog for all aspects of the sector, including employers who do the wrong thing.

The ROC came under heavy fire from Labor and the Australian Workers' Union over its role in an investigation of donations made when Bill Shorten was a union boss.