New post-Brexit trade rules must not be imposed on Wales without consent, the Welsh Government has warned.
UK government plans ask all four nations to accept rules and standards set by each other to ensure trade remains seamless across the UK.
The Welsh Government said it had not seen the plans and any system forced on Wales would be “deeply damaging”.
Plaid Cymru called Whitehall’s proposals a “power grab” and an undermining of devolution.
Under UK government proposals to be set out in legislation later this year, Scotland and Wales will acquire new powers in areas including food labelling, support for farmers and energy efficiency, currently regulated at EU level.
The UK government has however said that devolved administrations will have to recognise the rules of all four nations, so as not to harm trade within the UK.
In a policy paper, it says this will ensure a level playing field for all firms regardless of which UK nation they are in, to ensure a UK-wide “internal market”.
The Welsh Government said while it supported the principle of seamless trade any rules must be agreed by the devolved nations.
A spokesman said: “Any new system must have independent oversight and dispute resolution.
“Unfortunately, the UK government has not managed to share the paper with us, and Welsh ministers have had no recent discussions with the UK government on these issues.
“Any attempt to unilaterally impose a system will be deeply damaging.”
But Welsh Secretary Simon Hart said Wales was a “vital part” of the UK’s single marketplace and 75% of Welsh goods were consumed in the rest of the UK.
“Securing this internal market will ensure this trade remains seamless, safeguarding thousands of Welsh jobs,” he said.
“It is vital for our shared prosperity and our ability to bounce back from the pandemic that people, products, ideas and investment continue to flow unhindered throughout the UK.”
However, Plaid Cymru’s leader at Westminster Liz Saville Roberts said the plans were a “power grab” from the Conservative government.
“It is complete doublespeak to claim more powers are on their way to Wales when we know powers defined by the devolution settlement are being held in Westminster,” she said.
“It is simple – Westminster won’t give Wales the authority it needs to stand on its own two feet.”