A SIPTU spokesman has said a ballot of its 250,000 members on a day of industrial action has been completed tonight.
The results are expected to be known early next week.
The Irish Congress of Trade Unions has organised the one day strike on 30 March.
The stoppage will affect Government services and private sector companies which have not met the terms of the national pay agreement agreed last autumn or put alternative arrangements in place.
Unions must give seven days notice of strike action to employers, the deadline of which is Monday.
The SIPTU spokesman said local branches have been instructed to directly notify employers.
He added that initial feedback was towards industrial action.
Meanwhile, a spokesman for IMPACT said its ballot is complete and the results are due on Monday.
He said was too early to indicate figures.
Tonight, a spokesman for UNITE - which has 60,000 members, most of whom are in the private sector - said the results of its ballot should be known Sunday or early Monday.
He said employers would be notified by the deadline.
