Leading constitutional lawyers Professor Emeritus Cheryl Saunders and Professor Michael Crommelin and former Department of Finance economist Glenys Byrne have accused the federal government of exceeding its powers in running grants programs like the infamous Community Sport Infrastructure Grants scheme.

Professor Saunders said former Sport Minster Bridget McKenzie's intervention in the allocation of CSIG grants was unlawful and the way successive governments had set up and run such grants programs was "a complete abuse of taxpayers' money".

In a submission to Senate inquiry into the administration of sports grants, Professor Saunders and Professor Commelin said the Sports Commission Act severely circumscribed Senator McKenzie's power and the way she intervened in the CSIG program was "clearly inconsistent with the statute".

Professor Saunders said the sports grants program was also symptomatic of a broader problem in which the Commonwealth circumvented the states to provide grants directly to community groups.

Ms Byrne, who worked in Finance for almost 30 years, said this was a long-running issue.

She said successive governments had been "rather cavalier" in setting up and running grants programs without a head of power under section 51 of the constitution.

The issue reached the High Court earlier this decade when the federal government was challenged over its national school chaplains program.

After losing the case the Commonwealth created delegated legislative instruments to get around the problem, though Professor Saunders warned they were "not being used in the way described".

Ms Byrne said the result was an "absurd" situation which was "totally without integrity and totally ignoring the constitution".

She warned that discretionary grants programs in areas like sport, local government, environment, regional development and the arts were "notorious for entrapping ministers into acts of political greed, notably pork barrelling".

READ MORE:

"Once entrapped, there is then a strong incentive to try and cover up what are, in effect, egregious abuses of power and public trust," Ms Byrne said.

The former Finance official said that not only were such practices legally dubious and corrosive to public trust, the doling out by the federal government of small individual grants was "very, very inefficient".

Professor Saunders and Professor Crommelin said there were major constitutional issues at stake, and the Senate inquiry was a "watershed moment in which to take stock of Commonwealth spending practice before it gets further out of control".

"The Australian constitutional system relies heavily on the integrity and effectiveness of governing institutions," the constitutional experts said.

"These are jeopardised by the sports grants and similar programs, exacerbating the erosion of trust in public institutions which already is a matter for concern."