Porters at Ninewells are set to begin a complete and indefinite strike on April 7.
If the situation cannot be resolved, 117 workers will walk out of Ninewells and Victoria hospital in a dispute over pay.
Workers began their fifth week of industrial dispute today and claimed they have had no contact about resolving the dispute.
Unite union official Colin Coupar said: “Statutory notification was given to NHS Tayside on Friday that a complete strike is to take place.
“It is outrageous that it has had to come to this.
“For the last few weeks I’ve been dealing with management who are prepared to play with people’s healthcare.For more on this story, see Saturday’s Courier“This is happening because we don’t know what’s left to try.
“We have increased our efforts to get to some kind of settlement and offered arbitration and at this point we don’t know what else we can do.
“This dispute has been going for over half a year, and with each escalation we get no closer to any kind of agreement and at this point we don’t know what else we can do to persuade NHS Tayside to get round the table.”
Mr Coupar says the Union will support workers who were docked pay for taking part in industrial action.
“I’ve seen the docked pay slips of workers, some of whom are working full duties for three days and coming home with a pay slip of less than £80.
“We will be taking legal action against NHS Tayside for that.
“I have seldom come across an employer that doesn’t seem to have any interest in getting a dispute resolved.
“They will neither acknowledge their error nor produce the document they are simply in denial of the facts.”
Porters took strike action more than five weeks ago, firstly with refusing to perform some duties and short half-shift strikes, and two weeks ago began a series of 24-hour strikes.
They dispute that they are paid less than porters in other NHS Tayside hospitals, and have claimed they are the worst-paid hospital porters in Scotland.
NHS Tayside have not yet responded to the new threat,