The Scottish Government has rejected a deal aimed at ending a long-running Brexit dispute between Westminster and the devolved administrations - despite politicians in Wales giving it the go ahead.
Welsh Finance Secretary Mark Drakeford said changes had been put forward to the UK Government's EU Withdrawal Bill which would "protect devolution".
Like their counterparts in Scotland, ministers in Wales had previously insisted the Bill was a "power grab".
Now the UK Government is to make a number of changes, including introducing a "sunset clause" limiting how long devolved powers returning from Brussels will remain in London after Britain leaves the European Union.
But Scottish Brexit Minister Mike Russell said the amendments, due to be published on Wednesday, could still see Holyrood's powers restricted for up to seven years.
First Minister Nicola Sturgeon has made clear her opposition to this in a letter to the Prime Minister.
"This is not something I can recommend to the Scottish Parliament for approval," the SNP leader told Theresa May.
Mr Russell stressed the Scottish Government still wanted to reach a deal with the UK Government over the EU Withdrawal bill, but was clear ministers could "not agree at any price, and certainly not at the price of undermining this Parliament and the essential work it does for all the people of Scotland".
In a statement to Holyrood he said: "The key sticking point remains, as it always has been, clause 11 and the insistence of the UK Government on its right to take control of devolved powers."
Devolved powers returning from Brussels in the wake of Brexit would go first to the UK Government, so common frameworks can be established, but even with the "sunset clause" in place, Mr Russell claimed Westminster would have a "free hand to pass legislation" directly affecting matters such as fishing or the environment in Scotland for up to seven years, while Holyrood's hands would be "tied".
He said: "It would be an outrage if the UK Government decided to use what the people of Scotland did not vote for - Brexit - to undermine what we did vote for - devolution.
"The UK Government has no mandate to undermine the powers of the Scottish Parliament.
"And, therefore, the Scottish Government will do everything we can to protect the devolution settlement people voted for so overwhelmingly more than 20 years ago."
A spokeswoman for Theresa May said the UK Government had "put a considerable offer on the table that would see the vast majority of devolved powers automatically flow from the EU to Belfast, Cardiff and Edinburgh".
The spokeswoman added: "It's disappointing that the Scottish Government have not yet felt able to agree with our amendment but we remain focused on engaging constructively with them to provide the certainty needed and make sure all parts of the UK are ready for our departure from the EU."
She continued: "Tomorrow is the deadline for making changes to Clause 11 of the bill, so we need to table the amendment.
"These talks have been going on for a considerable period of time. They have been constructive and we intend to carry on talking."
Mr Russell dismissed suggestions the Scottish Government had been about to sign up to the deal, but had been vetoed by Ms Sturgeon.
Scottish Conservative constitution spokesman Adam Tomkins accused the First Minister of having "put her narrow nationalist agenda before the good of the country".
He said: "The Welsh Government has signed up to this deal. Yet Nicola Sturgeon, alone, refuses because she prefers to pick a fight with the rest of the UK in order to keep her obsession with a second independence referendum alive.
"She began using Brexit to push for that referendum on the morning after the vote, and she hasn't stopped trying since."
Scottish Labour Brexit spokesman Neil Findlay said: "Reports that a deal was on the table, only to be vetoed by Nicola Sturgeon, would be a betrayal of the Scottish Parliament's good faith.
"The fact the Government of Wales has reached an agreement but the Scottish Government has not is a real concern.
"It would be wrong for the SNP Government to play politics with devolution in order to further their goal of independence."