The federal government will be forced to offer low and middle income earners another tax cut or workers will have to fork out thousands of dollars extra in tax by the middle of the next decade.

The Parliamentary Budget Office has found the 6 million Australians earning between $23,000 and $64,000 a year will be pushed into higher tax brackets at five times the rate of the 2.6 million earning more than $100,000 by 2027.

Even after the Coalition's decade long $144 billion tax cut plan was passed by Parliament in June, an adult full-time median salary earner currently on $66,000 a year would be handing over up to $1000 a year extra to the Tax Office by 2026.

"The second and third quintiles are projected to experience the largest increases in average tax rates over this period," the independent parliamentary body found, rising 5 percentage points, compared to only 1 percentage point for the highest earners or fifth quintile.