The Scottish Greens could leave the Government if the new SNP leader “attacks and unravels” the policies of the Bute House Agreement, Patrick Harvie has warned.
The party is holding its conference amid speculation the power-share will not survive the race to succeed Nicola Sturgeon.
The Scottish Greens co-leader said any new leader would have to share their values or the deal would come to an end.
The Bute House Agreement sees the Greens support the SNP at Holyrood in return for policy commitments and cabinet positions.
Harvie, the active travel minister, said his party wanted to continue the agreement and he would “regret” if it came to an end.
But of the three SNP leadership contenders, only Humza Yousaf has vowed to continue the deal.
Harvie told STV News: “The Scottish Greens remain committed to fulfilling the Bute House Agreement.
“That’s a political cooperation agreement, not just between party leaders or co-leaders, but it was developed and negotiated between the parties and signed off by the party membership, both the Scottish Greens and SNP.
“We remain committed to that, not just the policies within that, but the progressive values it’s built on.”
He added: “But if [the SNP] were to nominate a first minister who doesn’t share those progressive values or who wanted to attack and unravel the good and progressive policies that are in that agreement they would effectively be bringing it to an end.”
The Scottish minister said he didn’t think that would ultimately happen, saying the agreement has been of “clear value” to both parties.
However, the Greens said that support is contingent on policy agreement with the SNP.
The party previously warned they would not support the incoming SNP leader if they did not challenge the UK Government’s decision to block Scotland’s gender reforms.
Kate Forbes has said she would look at any legal advice before challenging the UK Government and said she would have voted against the bill if she wasn’t on maternity leave.
Regan meanwhile resigned over her opposition to the bill.
Yousaf was steadfast in his support of gender reforms and had vowed to take the UK Government to court, but this week said he wouldn’t if he was advised the Scottish Government would lose the case.
Harvie said it was important any SNP leader challenged the UK Government on the decision.
He said: “I think we do need to challenge the abuse of the Section 35 power and yes of course, when you go into court you need to take legal advice, and it would be silly not to listen to it.
“But I think it would be an unrealistic scenario to be imagining that legal advice would be telling us that we wouldn’t have a chance.
“The legal arguments the UK Government is relying on are blown out of the water by their own consultation document just a few years earlier.”
Regan, the former community safety minister, said she would not take the UK Government to court over the issue.
In February, she said she was not afraid to pull out of the agreement with the Greens.
But she said she is willing to work with the Greens, saying she had contacted all the pro-independence party leaders.
She said the Greens were the only ones not to call her back.
Asked if he would get in touch with Regan, Harvie said: “Ash has been repeatedly claiming on television she’s spoken to us and that we’re very enthusiastic about her plans but that’s simply not true and I regret the fact she chose to misrepresent us in that way.
“She left a slightly garbled voicemail on my phone that didn’t really to be asking anything specific.
“But look, she knows where we are if she wants to contact us formally if she wants to.
“She hasn’t chosen to other than that slightly confused voicemail so I’m not entirely sure what she’s asking.”
Regan has been approached for comment.