Two major construction sites in Dublin have been brought to a standstill after crane operators from Unite union went on strike.
The Capital Docks project and a Cairn Homes development on Hanover Quay are the first sites to be hit by the dispute over pay.
The union says employers have failed to engage meaningfully in discussions.
Today's action at SISK on Capital Docks is the first in a series of rolling strike days.
However, Unite is planning to ballot crane operators in all Construction Industry Federation firms tomorrow for strike action.
That could mean a nationwide stoppage on construction sites by the middle of next month.
The situation has been exacerbated by a bitter inter-union dispute between SIPTU and Unite over who actually represents the crane drivers.
SIPTU has lodged a formal complaint against Unite with the Irish Congress of Trade Unions, which held a hearing into the row earlier this week. The outcome is awaited.
The CIF described the strike as irresponsible.
CIF Director General, Tom Parlon, said that within the past six weeks, the CIF agreed a pay deal with SIPTU giving crane drivers two extra hours pay per day for "greasing time" but that Unite is now seeking a further unaffordable claim.
He said construction companies had been caught in the crossfire of an inter-union dispute.