The council plans to close most of its services on June 2 and 3 and had initially instructed employees to take personal leave on both days.
The council’s chief executive Gerry Cornes has now designated June 3 a public holiday, which means anyone working that day will receive improved rates and all staff, regardless of whether they are due to work or not, will get extra time off.
However, those wishing to be off on June 2 will still need to use leave and Unison argues this is a breach of contract and discriminates against women and people with disabilities who are less likely to work Monday-Friday.
Local branch secretary Tommy Robertson said: “Our members are furious about the way this has been handled.
"The council have turned what should be a good news story and a chance for many to mark the Queen’s jubilee into an almighty stooshie.
"There has been no meaningful consultation let alone negotiation with Unison.
"That is why we now have the council using ridiculous language and telling our members they are ‘instructed’ to take their own leave, which should be their own choice.
“It is up to councillors to get this sorted immediately after the election. We saw neighbouring authority West Dunbartonshire get into a mess and councillors there sorted it, we need them to do the same here.
"We have written to leaders asking them to commit to act."
A technical note to elected members states: “The designation of June 3 as a public holiday is in direct recognition of the commitment of the workforce in responding to Covid and will not create a precedence for any future one-off public holidays going forward.”
Mr Cornes, said: “The council agreed at a meeting in November 2021 – in line with a number of other local authorities at the time – to mark the Queen’s Platinum Jubileeby awarding an additional day of no work requirement on 3 June, for all employees.
“This was subject to the continued delivery of essential front line services on that day with those required to work being entitled to time off in lieu at an appropriate later date.
“However, in light of the work and commitment of all employees in responding to the challenges of Covid over the past two years, and following further engagement with the trade unions, I have liaised with political group leaders and now intend to exercise my delegated authority to designate Friday, June 3, as a public holiday for the council.
“This means that anyone required to work on that day will receive enhancedrates in accordance with normal contractual conditions.
"In addition, those who work flexibly (whether in relation to the number of hours worked or work pattern) will also be credited with the appropriate leave.
“Employees will be required to take a day’s annual leave on Thursday, June 2,as previously advised.”