Department of Health deputy director of finance Peter Coates revealed the move at a Bombay conference last week.
Currently 132 trusts are signed up to the joint venture NHS Shared Business Services, which was set up between the NHS and outsourcing firm Xansa, and processes£15bn in payments annually.
Thirty-seven per cent of the work is carried out in a centre near Bombay, the remainder in four centres in the UK.
Last week, Mr Coates said he had given the joint venture permission to increase this to 60 per cent.
He is reported to have told a conference: 'It could go higher, but the constraint is that we cannot move jobs to India at the expense of shedding jobs in the UK. Politics will be an important factor.'
NHS Shared Business Services said it intended to expand the work carried out at the centre near Bombay to cover payroll, accounting and reporting transaction services.
Unison head of health Karen Jennings responded: 'To lose good people and to export British jobs is unacceptable. These are fairly low-paid workers who will be put out of work if it's sent overseas.'
She added: 'Many banks have taken the decision to bring back work from overseas because they haven't been delivering savings in the long-term.'
The DoH said the increase should not have any effect on existing staff in the UK, given that the business intended to increase the volume of its activity.
A spokesperson added: 'The rationale for increasing levels of off-shoring is primarily economic and will increase savings by£20m-£30m over 10 years.
'These savings will increase the amount that can be pushed back into the health service, in particular for frontline care.
'Unison was included on the Shared Business Services project. It was aware that work could be off-shored to India.'
A Xansa spokesman said the scheme would divert£224m into frontline care over 10 years.