Borders MSP John Lamont says farmers could lose out because of the way the Scottish Government plans to hand out CAP cash.
He is concerned all rough grazing land will be viewed as equal under the new payment system proposed, and not take into account the amount of livestock on the land.
And he fears it could result in some Borders farmers losing more than half of the financial support they receive now.
“Handing out equal payments for hectares regardless of productivity is simply unfair, and could punish larger farms.
“When these payments are vital to the future of these farms we cannot allow them to take such a large financial hit. We should be rewarding farmers who are capable of producing more and working harder, not taking money away from them.
“The SNP need to urgently rethink these plans.”
But a spokesperson for Rural Affairs secretary Richard Lochhead said: “This is complete hypocrisy from the Tories, who negotiated Scotland right to the bottom of the CAP funding tables for both direct farm payments and rural development funding - and it is Tory UK Ministers who want to eventually see an end to direct farm payments.
“The Scottish Government is currently seeking views on our proposals for implementing the new CAP, and encourage all interested parties to respond.
“We are taking industry concerns very seriously, and are open to suggestions for workable solutions.”