Tax Commissioner Chris Jordan told a Senate estimates hearing this week the ATO was looking to make assessments "based on best estimates" where companies gave insufficient information.

There were about 20,000 Uber drivers in Australia, with the number expected to rise noticeably this year after New South Wales joined the ACT in legalising the ride-share platform in December, while South Australia announced this month UberX would be allowed to operate from July.

Uber has paid about $400,000 corporate tax in three years, with the amount increasing more than ten-fold since 2013.

The sum paid in Australia has increased from $19,387 in 2013 to $249,280 last year, however about one-quarter of the fare paid for every Australian Uber trip is not taxed here.

A taskforce in the ATO to crack down on tax avoidance by large multi­national companies would be announced in next month's budget, it was reported on Friday.

All fares across Australia were remitted into the Uber Netherlands account via the app, with about 75 per cent of this then returning to the driver and becoming part of their Australian taxable income.

Uber Australia received costs plus 8.5 per cent from its Dutch parent, the company has previously confirmed. GST, however, is charged on the full fare paid.

The Australian offshoot of the US-founded giant and its drivers have come under the attention from the Tax Office since the government agency directed so-called ride-sharing drivers to collect GST from August 1 last year.

Uber has challenged that in the Federal Court, with a hearing set for July.

The ATO also reportedly wrote to about 15,000 ride-sharing drivers in December after comparing bank payments made by Uber with drivers' tax returns.

Uber Australia said in February it paid $1.25 million in payroll tax last year.

A Bloomberg report valued the global Uber business at more than $US62 billion in December.