Chifley introduced the higher tax system in 1943 to pay for the...

Chifley introduced the higher tax system in 1943 to pay for the aged pension and
other welfare benefits:

"The National Welfare Act 1943 stipulated that money for the National Welfare Fund would come from consolidated revenue.[74] As Chifley explained, it would be ‘an annual sum of £30,000,000, or a sum equal to one fourth of the total collections each year from income tax on individuals, whichever is the lower’.[75] The Government announced that it would raise the money for the National Welfare Fund by increasing income taxes. Lowering the income threshold at which tax became payable brought lower income earners into the income tax system.[76] According to law professor Geoffrey Sawer, Chifley’s tax increases faced strong opposition from the Labor left.[77]"
(aph.gov.au)