Assembly members will debate Welsh Government plans to by-pass the UK Government in the row over returning EU powers.
They'll discuss what's known as a continuity bill which ministers in Cardiff are rushing through the Assembly in the hope it will end the stalemate although it's also certain to set the two governments on course for a constitutional clash.
Today's debate comes the day before Carwyn Jones meets Theresa May who's described the bill as 'unnecessary.'
The Prime Minister will also hold one-to-one talks on Wednesday with the First Minister and his Scottish counterpart in Downing Street although I understand there's little prospect of agreement being reached.
There have been discussions between the governments at official level since last week's failed meeting of Brexit ministers. But I'm told there's been no new offer from the UK Government.
Despite the lack of agreement, the UK Government is pressing ahead with changes to its main Brexit law, the EU Withdrawal Bill, which is the source of the dispute.
UK ministers have put forward amendments to the bill which it says will mean that 'the vast majority' of powers being brought back from the European Union 'will now transfer directly' to the devolved administrations.
However tensions rose further last week when the UK Government listed the 24 responsibilities it says can't go straight to Cardiff Bay, nearly all of them affecting agriculture and the environment and which include the crucial issue of farm subsidies.
And a new area of disagreement emerged at the same time.
Alongside the list of 24 framework powers, a new list of 12 powers was published that the UK government doesn't think are devolved at all but which the devolved governments want included.
The publication of a leaked document explaining how those 12 were chosen has only added fuel to the fire and led to further claims that the UK Government doesn't respect the devolved administrations.
That charge is denied by the UK Government spokesperson:
Plaid Cymru will use the debate in the Assembly to urge the Welsh Government to stand firm. The party's leader Leanne Wood says Labour must 'do its job' and 'stand up for Wales.'