Post-Brexit trade deals must have the "broad consensus" of all four UK nations, First Minister Carwyn Jones has said.
It follows reports the International Trade Secretary Liam Fox has suggested devolved administrations should not be able to veto trade deals.
Plaid Cymru said no deal should be signed without the "endorsement" of the Welsh Government.
The UK government said it wants a trade policy that represents all of the UK.
The Times has reported that Mr Fox has written to cabinet colleagues setting out four options for negotiating trade deals.
The newspaper claims that he is understood to "favour options that do not give the devolved administrations a veto".
Mr Jones accused Mr Fox of "huge arrogance" but stopped short of calling for a Welsh Government veto on Brexit deals.
"It's massively important there's as much support as possible for any post-Brexit arrangements," he said.
"Liam Fox seems determined to work only for one part of the UK and not for all of it.
"We should have a very strong view. We should be part of the negotiation of these deals.
"A trade deal with some countries could affect Welsh farming directly so it is massively important that we are able to give our approval to trade deals and to be able to support the UK government with trade deals that work for Wales."
The First Minister added: "Devolution in Wales exists as the result of two referendums.
"The settled will of the Welsh people cannot be ignored any more than the EU referendum result."
He added future trading relationships with the EU and the rest of the world "needs the broad consensus of all the nations of the UK to be a success".
Plaid Cymru's treasury spokesman MP Jonathan Edwards said: "If the UK leaves the customs union enabling it to strike trade deals, it is vital that no trade deal is signed without the endorsement of the Welsh Government.
"Otherwise the British government could expose key Welsh economic sectors and our public services, effectively supplanting the devolved settlement."
The department for international trade said no final position had yet been reached.
A spokesman said: "We have been very clear that we want a trade policy that is inclusive and transparent and which represents the whole of the United Kingdom.
"We will not be giving a running commentary on possible future trade policy".
A Wales Office spokeswoman said: "We are committed to working with devolved administrations to ensure we deliver a deal that works for the whole of the UK. We will continue to liaise with them closely on this important issue."