Carwyn Jones and Nicola Sturgeon have set out a series of Brexit demands in a joint letter outlining the key points of difference with the UK Government over powers that will come back from Brussels after Brexit.
They claim that ministers at Westminster are taking powers which should go straight to Cardiff and Edinburgh.
The letter is to the Lord Speaker, who chairs debates in the House of Lords. Next week it will consider the UK Government's devolution amendment to the EU Withdrawal Bill, which the two First Ministers acknowledge does change the position but not by enough.
The two governments could not recommend consent to the amendment as it stands. They remain committed to working positively with the UK Government. The two governments would be pleased to put forward detailed amendments if it proves impossible to reach agreement with the UK Government.
Their suggested solutions point to where agreement might be possible -and to where it could prove very difficult.
They want the principle that their powers in devolved areas cannot be reduced or amended by Westminster without their consent to be enshrined in law, something which is regarded as an unacceptable "red line" in Whitehall.
Other ideas, such as "sunset clauses" to limit the time that devolved powers can be withheld might yet be part of the solution to the current constitutional impasse.
The two First Ministers also suggest that UK, Welsh and Scottish ministers prepare joint reports to their parliaments, which hints at a British version of the EU Council of Ministers that Carwyn Jones has previously suggested.