Welsh Cabinet Secretary for Energy, Planning and Rural Affairs, Lesley Griffiths, as well as Scottish Environment Secretary Roseanna Cunningham, have written a joint letter calling for the UK to determine long-term policy arrangements as soon as possible.
They have insisted that any approach must maintain accountability to devolved administrations and legislatures.
The concern for Scotland and Wales is that a tax would shift accountability for reducing emissions to England.
To remain in the ETS up to 2030, the UK and EU will have to sign an agreement allowing ties to be maintained in certain sectors – thus far, negotiations have failed to reach a suitable middle ground in this area.
Former Labour Chancellor Lord Alistair Darling and former Conservative leader Lord Michael Howard say the upcoming Budget announcement is an ideal opportunity to announce an economy-wide carbon tax for the UK.