Plaid Cymru's Arfon MP Hywel Williams made his calls ahead of the second reading of the EU Referendum Bill in the House of Commons on 9 June.
Mr Williams said contingencies must be put in place for common agricultural policy and structural funds payments in the event of a vote to leave.
The loss of these funds would be "catastrophic", he said.
Mr Williams, Plaid's foreign affairs spokesman at Westminster, said the government must "urgently" set out their intentions.
"To suddenly cut off vital funds to our farming communities would also potentially decimate the agricultural industry here - a cornerstone of the Welsh economy," he added.
An MP has called on the UK government to set out contingency plans on "vital" EU farm funding to Wales.