It comes after the union called on the ACT government to pull its share of funding for Radford College following a $4 million donation for sport facilities upgrades.

Philanthropy Australia chief executive Sarah Davies said any donation should be encouraged.

"I commend the family for being generous with their private wealth and I commend them actually for being public about it because I actually think giving is really good and we have really good regulation in Australia that protects charitable giving that makes it accountable that makes it legitimate," she said.

Ms Davies said individuals could only make a tax-deductible donation through a school's building fund, library fund, or scholarship fund or through the Schools Plus charity which distributes funds to disadvantaged schools around Australia.

She said independent schools did tend to get more donations than public schools.

"That raises questions actually that are much more fundamental about the kind of community that we want to live in and the sort of civil infrastructure that we that we want and really comes down to matters of public policy around educational investment."

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Australian Education Union ACT branch secretary Glenn Fowler said until the needs of public schools were being met, government funding for private school should be reduced or removed.

"It's not a needs system while we accept that nothing changes when a huge private donation goes into a school," he said.

"By segregating students based on family income, private schools are creating greater inequality."

Association of Independent Schools of the ACT executive director Andrew Wrigley said the government should support a child's education no matter which school they attend.

"This should never be considered as a war. This is about providing what is best for kids in any school setting."

Mr Fowler said the union would repeat its call for government funding to be reduced every time a large donation was made to a private school.