Australian tax officials have been told to prepare for a campaign to recover student and trades training loans from graduates and trainees living and working all over the world.

But ex-pats need not fear a call from debt collectors, the ATO says, with an approach of encouraging "voluntary compliance" preferred, at least in the early days of the new rules.

Graduates and other workers who have covered their uni fees with HELP loans, previously known as HECS, or Trade Support payments are currently not required to make repayments if they are not living in Australia.

The government believes more than $30 million in repayments is lost each year from former students and tradespeople who complete their studies or training and then jet-off overseas, beyond the reach of the Australian Taxation Office.

But on July 1 the rules change and Commissioner of Taxation Chris Jordan has told his 19,000 public servants that the ATO intends to harness social media to let Australians living in the UK, Japan and Canada know they are are back on the hook for their HECS debts.

All Australian graduates living offshore and who have with HECS, HELP, or TSL debts, will have to declare their "global income" the ATO each year.

If they are earning more than $53,000, they will have to start paying back their loans, under legislation passed by the Coalition government.

A 2016 report by the Parliamentary Budget Office said 19 per cent of HELP loans were "doubtful", or unlikely ever to be repaid, and that figure was forecast to rise to nearly 22 per cent by 2025-26.

Nearly $2 billion worth of student loans were being written-off each year and that number was expected to double to $4 billion by 2026, the PBO said.

In his regular newsletter to ATO staff, Mr Jordan told his workers that the preparations for the first steps of the global debt collection effort were already underway.

"For debtors living overseas with a Higher Education Loan Program (HELP), previously known as HECS, or a Trade Support Loan, their loan probably seems a million miles away," Mr Jordan told his public servants.

"From 1 July 2017, HELP and TSL debtors who are non-residents for taxation purposes with either a new or existing loan will need to declare their worldwide income to the ATO.

"If their worldwide income is above the minimum repayment threshold they will need to make a repayment towards their loan."

Mr Jordan said there would be a number of ways to get the message to Australians living abroad that they were no longer on a student loan repayment holiday.

"Overseas debtors will be informed of these new measures before 1 July through, advertising on social media and online targeting debtors in the UK, US, Canada and Japan," the Commissioner told his workforce.

There would also be emails going out to individual debtors where they could be identified but an ATO spokesperson said the Tax office would prefer an approach of encouraging voluntary compliance with the new regime.

"The Australian taxation system is underpinned by voluntary compliance of individuals with their taxation obligations," the spokesperson said.

"This extends to the overseas debt recovery measure where Australian student loan debtors living overseas are encouraged to voluntarily comply with their obligations to repay their HELP or TSL debt."