Union leaders have accused Ceredigion County Council of having a "hidden agenda" over the closure of Awel Deg residential home in Llandysul.
They also claim the council has discussed selling the home off to the private sector.
In an open letter to council leader Ellen ap Gwynn Unison regional organiser Jeff Baker and GMB regional organiser Althea Phillips claim the council has responded to calls to re-open the home in "a disingenuous manner". They add "there has been a pre-determined decision and hidden agenda with the deliberate intention of closing the home and making the 40 staff redundant."
The council closed the 26-bed home in February after the number of residents fell to seven.
Unions say the temporary closure was "unnecessary" and has raised questions over the home's future.
The unions claim that the council gave a committment they would re-open the home under local authority control. "However, the trade unions have seen council documents that show that discussions took place on December 2013 on selling off the home to the private sector," says the letter.
They also claim the council said back in February that building work would take six months and then changed that to a year when the trade unions made a case for staff to remain employed.
The unions are now calling to put their case before a meeting of full council - despite an earlier call being refused.
A council spokesman said: "The Leader is extremely disappointed to receive this letter. There were valid reasons for the temporary closure of Awel Deg Residential Home and it became imperative for the Council to respond swiftly and decisively."
A full review is now being made of all care homes in the county.
"The council has no hidden agenda and the unions have received assurances that Awel Deg will be re-opened in April 2015 as a dementia care home.
The Unions are also fully aware that the Council is doing everything possible to seek suitable alternative employment."