According to reports in The Independent, Pricewaterhouse Coopers and KPMG have given the Tories around £500,000 since the start of 2008 in an attempt to build ties with the party.
The donations were not made in cash but through the use of staff and services.
Meanwhile, there are reports that the Tories are working on proposals to set up a funding body to boost economic recovery for if they get into power.
Shadow business secretary and shadow Chancellor George Osborne are believed to be working with a group of entrepreneurs and financiers.
They are looking at how to fund small businesses and how to boost lending in the banking system.