Business Secretary Vince Cable says there is no question of the UK government imposing lower pay on public sector workers in Wales.
During a visit to Wales, he said the Westminster coalition was considering more local "flexibility" in wages.
Campaigning for May's local elections, he attacked "wildly exaggerated stories" about regional pay.
Labour and Plaid Cymru are opposed to the idea, as are Conservatives and Liberal Democrats in the assembly.
The Treasury says bringing pay into line with local businesses will help private companies grow in places where they compete to recruit staff with public sector employers.
In the Budget Chancellor George Osborne said some departments could move to local rates of pay for civil servants when wage freezes end.
But with estimates that Welsh workers can expect to earn up to 18% more in the public sector than in the private sector, the coalition's opponents say Wales stands to lose out.
Mr Cable told BBC Radio Wales: "There's absolutely no question of the UK government imposing lower levels of public sector pay on Wales or other relatively low income parts of the UK.
"It would be wrong to do so and it's practically impossible."
The Liberal Democrat cabinet minister was in Cardiff on Wednesday where his party hopes to retain its leadership of the local council at next month's elections.
Freezing public sector salaries until they fall into line with the private sector would be "crude and broad brushed", Mr Cable said.
"At the moment all that's happening is that the government is looking at evidence and looking at ideas about how we might get more flexibility into the system in a sensible and fair way," he said.
The previous Labour government had done the same for staff working in the courts service, he added.
Politicians from across the assembly chamber, including those from Mr Cable's own party, have voiced their opposition to the prospect of regional pay deals.
Campaigning in south Wales, Labour's First Minister Carwyn Jones said "people simply don't trust the Lib Dems".
"Today's comments on regional pay from Vince Cable show why this is the case. He is part of a UK government that wants to introduce regional pay for public sector workers in Wales, cutting wages in some of our poorest communities."
Plaid AM Lindsay Whittle said: "We want to see public sector pay and conditions protected and we believe that this will only happen if they are devolved - so that it is a Welsh government, directly accountable to the people of Wales that is responsible for making the decisions."
Tory assembly group leader Andrew RT Davies said: "We have not seen any evidence of the benefits of a regional pay system."
He said Plaid's policy of independence and a Labour proposal for a regional benefits cap were "real threats to levels of pay in Wales".