The Conservatives have outlined plans to make the tax system simpler for small businesses.
Mr Osborne says NI and income tax systems are too complex
Shadow Chancellor George Osborne said VAT, income tax and National Insurance were too complex and create too much paperwork for businesses.
The Tories have asked accountancy firm Grant Thornton to look at aligning the administration of NI and income tax.
But he was accused by the government of offering an unfunded "wish list of tax cuts" to the party's right-wing.
Mr Osborne told an audience of businesspeople in London the Conservatives would try to reduce the tax burden on small businesses, in return for them encouraging more flexible working.
Raising NI and income tax contributions using different systems, and over different periods, was causing "needless complexity and administrative difficulties", he said.
The Conservatives are looking at aligning the charge period to ease the "regulatory burden".
Grant Thornton will also review the documentation, information and administration required for VAT.
"Streamlining the Byzantine intricacies of VAT administration will make a real difference to small businesses all over the country," he said.
He also questioned the value of tax relief on investment announced in the last Budget, saying some companies would not be eligible, while others would need to hire expensive tax advisers to make claims.
"The Conservative Party will continue to oppose the chancellor's latest tax rise for small businesses. We are fighting this measure every step of the way in Parliament," he said.
But Chief Secretary to the Treasury Stephen Timms said Mr Osborne should "come clean" about his plans and spell out how he plans to pay for his pledges.
He added: "After caving in on grammar schools, David Cameron and George Osborne are now promising the Tory right a wish-list of tax cuts - without any idea how to fund them.
"If they ever got the chance to implement these uncosted, up-front tax pledges, the result would be a return to boom and bust in our economy."