BORD na Mona workers have begun a two-day strike over a 3.5pc pay rise.
Unions at the state-owned peat producer ramped up the industrial action today with a halt to harvesting in Longford, Westmeath, Laois, Offaly, Kildare and Roscommon.
Pickets were also placed at briquette factories in counties Offaly and Tipperary and at Edenderry power station in Co Offaly.
ESB power stations will not be disrupted in the action, but briquette production will.
The Group of Unions took a decision to escalate the dispute earlier this month.
The unions SIPTU, UNITE and the TEEU struck a deal with management on the 3.5pc pay rise earlier this year.
However, the deal was rejected by staff, who balloted in favour of industrial action.
It is understood that the deal, agreed last April, would have meant staff got a lump sum payment of €1,000 upfront and a 1.75pc pay rise.
However, they were not guaranteed the final 1.75pc increase, as it depended on the company's performance. Based on the average yearly salary at the peat company of €44,800, the full 3.5pc increase would bring wages up to €46,368.
Bord na Mona said the latest plan of action was an "unhelpful escalation of action that will only damage the interests of the company and its employees".
Secretary of the Group of Unions Oliver McDonagh said the deal was rejected by members because there were implications for their pensions.