Leaders of the Unite union, whose members include 100,000 NHS staff, have questioned whether contracts awarded to private providers offer value for money and called for greater transparency over how companies secure NHS work.
The union has asked House of Commons health and social care committee chair Dr Sarah Wollaston to investigate 'how Virgin and other private healthcare companies have acquired such a plethora of NHS contracts'.
A Virgin Care spokesman said it won contracts through 'open procurement processes' run by CCGs.
Calls for scrutiny of the role of Virgin and other private providers in the health service come amid concerns about the impact of outsourcing public sector services. GPs have criticised long-standing problems with the primary care support service outsourced to Capita, with the BMA calling for the service to be brought back 'in-house' by the NHS.
The collapse of outsourcing giant Carillion has also fuelled concerns about private sector involvement in public services.
GPonline reported earlier this year on an Essex GP practice run by Virgin Care, which went from an outstanding to inadequate CQC rating in 18 months despite increased funding. Virgin Care currently runs 21 NHS primary care services, including GP practices, walk-in centres and other facilities - most of which it says are rated 'good' by the CQC.
Virgin's full NHS portfolio - estimated at around £2bn by The Guardian earlier this week - includes a wide range of services covering children's services, flu jab programmes, adult social care and community healthcare services.
Unite head of health Sarah Carpenter said: 'With the spectre of Carillion still haunting the public sector the select committee needs to urgently examine whether the NHS and taxpayer is getting value for money from Virgin Care accumulating so many health service contracts.
'The scope of such an inquiry should be widened out to look at private healthcare companies, and the scale and scope of their involvement in the NHS generally as well as the potential impacts and risks that this may have.'
A Virgin Care spokesman told GPonline: 'For more than 10 years, we have been supporting the NHS and local authorities to deliver high quality health and care services; in that time we have saved the taxpayer millions and delivered the plans the NHS has asked us to, improving services for patients – 93% of people rating our services say they’d recommend them.
'When we bid to run services, we do so as part of open procurement processes run by GP-led NHS commissioning groups which consider both the quality of service being offered, value for money and track record to pick the best provider for their local population.'
In a letter responding to coverage in The Guardian earlier this week, Virgin said that its owner Sir Richard Branson 'has not and does not intend to ever take a penny out of the NHS' - and that any dividends would be put back into services.