As many as 400 staff have been issued with the letters after they staged an unofficial walkout from Glasgow's three homelessness centres yesterday - bringing the service to its knees.
The first action of its kind to hit the city council in nearly a decade rapidly escalated and spread to the authority's homeless accommodation units, where up to 100 members of staff were involved.
The council has also threatened the union Unison that unless it declares that the strike is being carried out with no authority then it will be sued.
The council is also drawing up contingency plans to deal with the likelihood of other staff becoming involved.
Official sources said the action was triggered by a female staff member who refused to take on a case involving a 16-year-old youth and was sent home.
Staff insiders said the demand on the woman was a breach of an agreement struck with management over staff shortages.
Efforts to resolve the situation include offering to reinstate the suspended worker on the basis she resumes full duties with no disciplinary action taken.
The council said the "priority will be to provide a level of response for homeless individuals which meets urgent needs". A spokesman added: "This unlawful industrial action is completely unacceptable and those involved are liable to be dismissed if it continues.
"Unlawful industrial action is putting unnecessary pressure on the homelessness service and if this strike is not formally repudiated by Unison immediately we will consider seeking damages from them."
Glasgow is being forced to make £42.6 million in budget cuts, with social work and education bearing the brunt.
Unions have been involved in a long-running grievance with social work management over increased workloads stemming from frontline posts being left empty.