Thousands of hospital staff around the country are expected to announce today their intention to strike.
SIPTU has been balloting workers in health service support grades in 36 hospitals in a dispute over pay.
The result of the vote will be revealed this morning.
Paul Bell, the union's health division organiser, says early indications are in favour of a strike in June.
"At this stage, it looks as if over 14,000 people have been balloted, which is a fairly widespread ballot all over the country," he said.
"Early indications are that members are going to vote for strike action and industrial action but at this stage, it is not known by what amount.
"What's at dispute is that support staff members of SIPTU employed in the health service, many of them have undergone a job evaluation process," he said.
"The bulk of the members are employed as healthcare assistants, laboratory aids and operatives, and those members have been deemed to be upgraded through an independent evaluation service which would lead them to be paid at a higher band than they currently are."