Deputy Labor leader Susan Close, a member of the former government that established the state-based inquiry with powers to compel witnesses nationally after allegations of upstream water theft and rorting, declared the move a “betrayal”, with SA Best MLC Frank Pangallo warning it was “just designed to blow this inquiry out of the water”.

Attorney-General Vickie Chapman today declared the High Court action a test case which, while it wouldn’t immediately impede the operation of the commission, would have major ramifications for any future inquiries of this sort.

“What’s important is we’re now being asked to consider whether, as a party to an intergovernmental agreement, we have the capacity to inquire into it as one of the parties signed up – and secondly, whether there’s an enforceability capacity,” she said.

“It’s big picture – it needs to be dealt with… it will have some significant effect in relation to the future of national intergovernmental agreements and how we operate them.

“And it may have implications in relation to each of the state and national royal commission acts.”

The High Court bid was announced late yesterday, with the Commonwealth and the Murray Darling Basin Authority seeking to stop their own staff from being summonsed to give evidence to the commission helmed by Bret Walker SC.

In a joint statement, both confirmed they have been served with summonses to appear before the royal commission, which holds its first public hearing in Adelaide next week, and said “the Commonwealth and MDBA’s view is that the royal commission cannot compel the Commonwealth or the MDBA to provide documents or give evidence.”

“The decision to commence these proceedings is not about water resources, the content of the Water Act 2007 or the content and implementation of the basin plan… there are broader matters at play here,” the statement said.

Chapman told reporters today: “Obviously they’ve given notice they don’t want to comply with the compelling of those witnesses… Mr Walker’s view [is] that he has the power to do it.”

She said while it was “not unusual” to test “issues of overlapping jurisdiction” in the High Court, the outcome of the case would have major ramifications for future federal agreements – and disagreements.

“In future, how are we going to inquire into the progressing of these, and how are we going to enforce them if that’s necessary – and who should do that?” she said.

She said Walker would “continue with the commission in the meantime” but that “as a matter of respect an undertaking has been given to the Commonwealth that pending the High Court matters being determined he won’t exercise his powers in relation to seeking a warrant be issued”.

Close declared the High Court bid “an act of treachery”, given SA Liberal Senator Anne Ruston had declared upon the inquiry’s establishment in November that “certainly the Commonwealth will cooperate… we haven’t got anything to hide”.

“Will Steven Marshall stand up to east coast irrigators and stand up to the Commonwealth government on behalf of SA?” Close said today.

Pangallo declared the bid “an act of treachery and bastardy by the Turnbull Government, designed to undermine the SA royal commission”.

“How can Bret Walker conduct an inquiry without taking evidence from MDBA and Federal Government staff?” he said.

“It’s just designed to blow this inquiry out of the water, and it will end up being a waste of money because we’ll never be able to get to the bottom of it all.

“If this proceeds to the high court Bret Walker’s inquiry is basically going to be redundant.”

He echoed Close’s comments that “there’s a big test here for Steven Marshall, who will need to put pressure on Federal Government ministers”.

“We need to find answers and this is the only way we’re ever going to do it,” he said.

“SA plays a vital role in the Commonwealth… we’re a vital part of this Murray Darling Basin plan. We should be able to get answers and information that will show where we stand under this plan.”

SA Greens senator Sarah Hanson-Young also weighed in, accusing the Federal Government and MDBA of “attempting to corrupt the SA Royal Commission” in “an appalling act of secrecy that shows [they] have something to hide”.

“Applying to the High Court to seek an injunction to prevent officials from giving evidence at the South Australian Royal Commission is not how you restore public confidence in the plan,” she said in a statement.

“The Government and the Murray Darling Basin Authority are favouring secrecy over transparency when it comes to their mismanagement of the Murray Darling Basin Plan. Their protection racket has got to be busted open… banks don’t get to just ‘opt out’ of appearing before the Banking Royal Commission.”

A statement from the Royal Commission said it would continue with its scheduled hearings and would not comment “as the matter is before the courts”.

“The Commissioner will not take any active part in those [High Court] proceedings,” it said.