More than 4,000 health workers employed in Eastern Regional Health Authority hospitals, including 200 ambulance crew, are balloting on whether to strike over pay arrears.
The workers, who include cleaners, caterers, care attendants and porters, took similar action last year and were promised improvements in pay.
A SIPTU branch secretary, Mr Paul Bell, said these had not been made. Members are expected to vote overwhelmingly for a strike, likely to begin on March 29th.
More than 100 staff at workshops for people with learning disabilities in the Eastern Regional Health Authority (ERHA) area are beginning a work-to-rule today because of delays in implementing a pay increase.
Mr Bell said part of last year's agreement was that discrepancies in pay of £10 or more would be corrected within 24 hours. This was not happening, and other problems had arisen.
SIPTU members were still waiting to be paid an increase of £19.46p a week with arrears dating from last October. Ambulance crews were due an extra Sunday premium payment "for some months".
What made the situation worse was that voluntary and private hospitals had made the necessary pay adjustments, but the ERHA had failed to honour commitments in its own institutions.
Both sides will meet today to discuss the dispute, and emergency cover if it goes ahead.
"It was bad enough dealing with the Eastern Health Board, but since it was split into three health boards and the ERHA set up, the problems have multiplied," Mr Bell said.
A spokeswoman for the three eastern health boards said it was not always possible to identify errors in pay within 24 hours, but as soon as they were identified they were rectified immediately.
On the analogue payments, she said the Department of Health and Children had sanctioned the rise only in January. The new rates would be paid from March 29th and arrears in April.