Wales' environment secretary has accused the UK government of being determined to pursue a "constitutional conflict" within the UK over Brexit.
Lesley Griffiths called the Brexit bill an attempt to "bypass devolution" and "constrain" Wales' powers over farming and the environment.
She is due to meet her Westminster counterpart Michael Gove on Monday for an update on EU talks.
He has said Wales could have its own agricultural system after Brexit.
Ms Griffiths, who was at the NFU Cymru conference in Llandrindod Wells, insisted that the Welsh Government would not accept the EU Withdrawal Bill in its current form and called on UK ministers to offer more "clarity and certainty" for Welsh farmers.
She said it was "unfortunate" that Mr Gove had only attended one meeting of a Joint Ministerial Council working group on the environment since being appointed in June.
The two environment secretaries met for the first time at the Royal Welsh Agricultural Show in July, when Mr Gove described relations with the Welsh Government as "fantastic".
Addressing Westminster's Environment Audit Committee this week, he told MPs that devolved nations could have their own agricultural systems and fund them accordingly after Brexit, provided negotiations surrounding access to the EU's single market and other trade deals were not infringed.
NFU Cymru president Stephen James urged the UK Government to avoid a "no deal" Brexit scenario, which he said would have "severe implications for Welsh farmers".
The industry was "fast running out of patience" with both UK ministers and the European Union over how negotiations were going, he claimed.
He called for the UK to remain a part of the Customs Union, until a comprehensive free trade agreement had been secured.