Nick Gibb, the shadow schools minister, said commission guidance to schools was too prescriptive and should be relaxed to allow a wider range of options than means-tested bursaries.
"It is right that independent schools, which enjoy charitable status, should meet a public benefit test, and there are a number of ways in which they can do so," he said.
"They can share teachers, allow access to playing fields and, if a Conservative government is elected, it will be far easier for them to open up state sector counterparts that will particularly help children in the most deprived areas.
"We want independent schools to continue the excellent contributions they're currently making, but we must make sure the public benefit test does not become too bureaucratic."
The commission's guidance to schools is based on case law in the light of current economic and social circumstances. A Conservative spokesman declined to say whether a future Tory government would direct or encourage the commission to alter its guidance.
Rosamund McCarthy, a partner at law firm Bates Wells & Braithwaite, said that any attempt to enforce a different interpretation of public benefit would be resisted by the commission as "political interference with an independent regulator".
A spokeswoman for the commission said: "Our guidance sets out the framework for all charities, not just schools, for meeting the public benefit requirement. This framework, based on case law, allows for considerable flexibility in approach for charities, as our first assessments of charities have shown. We continue to work with schools and their representative bodies to help them understand and show the public benefit they bring."