Plans to peg public sector pay to local wages are "unlikely to succeed" if opposed at the Liberal Democrat conference, a senior member of the party has warned.
Deputy leader Simon Hughes made the prediction ahead of party members voting on the controversial public sector reform in Brighton next week.
Lib Dems in South East Cornwall have tabled a motion demanding that local and regional pay proposals are jettisoned.
Critics claim that ending uniform pay for teachers, nurses and other public sector workers threatens to strip tens of millions of pounds from the region's economy. The low-wage Westcountry would be hit hard as public sector jobs are among the best paid.
Speaking at a pre-conference briefing at Westminster, Mr Hughes said there was a "perfectly valid" economic argument to be made for differential pay.
But he added: "There was a fairly early and robust response from many in the party saying 'no we don't think that's the right thing to do'.
"This is the first opportunity since then for the party to take a view in the light of the debate.
"My judgment is that this will be passed as a motion. I assume because of the strength of feeling expressed, not just in Wales and Scotland, but the regions of England."
Mr Hughes went on: "The party forms its policy. Everything we decide as policy since the election goes into government ministers and they will seek to deliver as much of that as possible."
However it would send a message to senior Lib Dem cabinet members including Deputy Prime Minister Nick Clegg, Chief Secretary to the Treasury Danny Alexander and Business Secretary Vince Cable.
He said: "Obviously it takes two to make a coalition policy in the present government. We can't promise we can deliver everything.
"But if this motion is passed it will give a very clear steer to Nick and Danny and to Vince it wouldn't be an acceptable policy to us and I imagine that means it would be unlikely to proceed."
The motion to be debated by activists highlights concerns that regional pay could "adversely affect" many areas, taking money out of the local economy, hitting businesses, and acting as a "brain drain".
While unlikely to directly impact on the row currently raging over separate proposals by 20 health trusts across the South West to introduce regional pay for NHS workers, it could serve to rally opposition further.
Hospitals in Plymouth, Truro and Exeter are among those signed up to the South West Pay, Terms and Conditions Consortium, which has been branded a cartel by critics.
The Government has asked the independent pay review bodies "to consider how public sector pay can be made more responsive to local labour markets".