Thousands of Scotland's council workers could walk out weeks after the independence referendum in a pay dispute which may cost almost half a billion pounds to settle.

Trade union Unison is to ballot 70,000 members across 32 local authorities in September with strike action scheduled for the following month if staff reject a 1% pay deal.

In a departure from previous demands for percentage rises, union leaders have indicated they now want an additional £1 an hour for every worker.

Scotland's 250,000 local authority employees typically work a 35-hour week, meaning each of them would be in line for an additional £1872 a year. The total bill to the taxpayer could be £468 million.

Douglas Black, Unison's regional officer for local government, said: "When you look at it in hard cash, £1 an hour doesn't seem to be a huge amount of money, but when you add it up over a period of a week, they can relate that to being another £35 or £36 a week in their pay packet.

"It's quite easy for them to work it out and to say, well, that might be worth a weekly shop or something like that. So it is a lot but in many ways it's been developed on the basis of also highlighting how far behind local government workers' pay has fallen in relation to inflation over the last five or six years."

Council umbrella body Cosla imposed a 1% rise for 2013-14 and 2014-15 after talks with unions reached a stalemate last year.

Unite and GMB took the deal but Unison leaders dug their heels in and held a consultative ballot in July, when 65% of a 22% turnout of members voted to support plans for an industrial ballot.

Black said: "Clearly Cosla's view was that the matter was closed, given that the other two trade unions had, in fact, accepted the two-year deal at different points between September and November last year. That is still their position.

"So it's going to be difficult to win this, given the employer's position. We have offered to meet with them and to be fair to them I think they will take up an offer of a meeting but I don't really have any high hopes it will move things forward in a way that could avert the ballot."

Voting begins on September 9, just days before the independence referendum. The ballot will close on September 29 and Black is determined to see the dispute through, whether or not Scotland votes to go it alone.

He said: "It's very interesting times with September 18 on the horizon. Our ballot obviously covers that period. I suppose the common held view is that, if there was a Yes vote in the referendum there will be negotiations over a period of, I don't know, 18 months or something like that, before Scotland becomes independent."

Should Scotland vote for independence on September 18, a walk-out by 70,000 council workers during intense negotiations over the future of the country will be an unwelcome distraction for the SNP.

A spokeswoman for Local government Minister Derek Mackay said: "Within tight current budgetary constraints, we have set out a distinctive pay policy for Scotland that aims to be fair and affordable.

"In contrast to the UK Government, Scottish ministers' pay policy targets support for those on the lowest incomes, including a commitment to the Scottish living wage and a minimum pay increase above 1% for those earning less than £21,000.

"We have made clear that, with independence, the Scottish Government would bring an end to Westminster's austerity, support our public services and establish a Fair Work Commission to ensure the minimum wage rises by at least inflation."

Cosla's human resources spokesman, Billy Hendry, a Conservative councillor in East Dunbartonshire, insisted Unison has "no legitimate grounds" for the ballot.

"I would urge caution on its part," he said. "Unison is part of the Scottish Joint Council bargaining machinery together with the GMB and Unite, both of whom welcomed the pay settlement. For Unison to now claim that they don't recognise the settlement for 2014-15 is disappointing and will be ultimately futile.

"The claim that they have a mandate for a future ballot from their membership is at best, questionable, with only 22% of those eligible to participate in a restricted ballot responding.

"Unison would do better to focus attention on the next pay round, negotiations on which will begin this autumn."