The dispute by crane operators looks set to spread after the Unite trade union decided to ballot crane drivers employed on sites of firms belonging to the Construction Industry Federation.

Yesterday two major sites in Dublin were shut down after crane drivers went on strike in pursuit of a significant pay rise.

At that point the union had only balloted members employed in non-CIF companies and agencies.

However, they have now decided to extend the ballot to those in CIF firms - raising the prospect of a nationwide shut down of construction sites by mid-July.

The ballot will be completed by Wednesday.

SIPTU has lodged a formal complaint against Unite for poaching members with the Irish Congress of Trade Unions, which held a hearing into the matter earlier this week.

The outcome is awaited.

Speaking after a meeting of crane operators today, Unite Construction Regional Officer Tom Fitzgerald accused the CIF of seeking to boost members' profits by depressing workers' pay.

He said that profits per employee in the construction sector had more than doubled since 2012 - while wages remain below 2004 levels.

Unite claims to represent 90% of crane drivers, though that is disputed by SIPTU which has traditionally represented the grade.

The CIF has described the Unite claim as unsustainable and irresponsible.