Tonga is one of the three major suppliers of labour to the programme.
But restrictions on travel to New Zealand and Australia and the ban on international flights in a number of Pacific nations, including Tonga, could mean that thousands of workers may be unable to take up positions this year.
Equally large numbers could be trapped as their work visas come to an end.
Australia’s seasonal work programme grew by 44% in 2018-19, or by some 3000 workers, after a cap on workers numbers was removed.