AMs will vote on Tuesday afternoon whether to fast-track a law to prevent what Welsh Government ministers have called a post-Brexit "power-grab".
The bill would bring devolved powers currently wielded at EU level to the Welsh Assembly.
It has been proposed by Cardiff ministers amid a row with the UK government over a key Brexit bill.
UK ministers have promised most powers in devolved areas will come to Cardiff – but agreement has remained elusive.
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The vote in the Senedd will ask AMs to back the introduction of what has become known as the Continuity Bill as emergency legislation.
This means it will pass through the assembly quicker than usual. If the timetable is agreed, the bill could clear the legislative process by as soon as 21 March.
It is expected the proposal will pass with Labour and Plaid Cymru support, although the Welsh Conservative group intends to vote against it.
UKIP AMs will have a free vote.
The proposed law is the Welsh Government's insurance policy against plans included in the UK government's EU (Withdrawal) Bill, currently making its way through Parliament.
Under the withdrawal bill's current plans, powers in devolved areas such as agriculture that are currently operated in Brussels are due to flow back to Westminster rather than Cardiff, Edinburgh and Belfast.
It has led to months of negotiations between UK, Welsh and Scottish government ministers about changing the bill.
UK Cabinet Office Minister David Lidington said, in a speech last week, that a "considerable" offer had been made to amend the bill, which would see the vast majority of the powers returning from the EU going to the devolved administrations.
But the proposals have been rejected by the Welsh and Scottish governments for not going far enough.
The discussions are set to continue, and Welsh Government is asking AMs to agree to fast-track the bill so it can be passed before the withdrawal bill is passed into law by MPs in Westminster.
At least one academic has warned that the bill could lead to a Supreme Court challenge from the UK government. Scottish ministers have also proposed similar legislation.
Welsh Finance Secretary Mark Drakeford and Scottish Brexit Secretary Michael Russell will meet Mr Lidington on Thursday, ahead of further talks between the first ministers of Scotland and Wales, and Prime Minister Theresa May on 14 March.
Speaking ahead of the debate, First Minister Carwyn Jones said: "The Continuity Bill is not an attempt to frustrate or block Brexit.
"We are simply seeking to protect our devolution settlement, while making sure there is legal certainty when the UK leaves the EU. This is what Welsh businesses are calling for."
A bill was previously proposed by Plaid Cymru's Brexit spokesman Steffan Lewis last year. His proposal received unanimous backing in an assembly vote in January.
Ahead of the debate, Plaid Cymru said it was "the prime minister's final chance to guarantee that Welsh powers will be protected post-Brexit."
A UK government spokesman has previously said that a Continuity Bill was unnecessary and that it would be better for the Welsh Government "to concentrate on reaching an agreement on the withdrawal bill".