A pay dispute involving thousands of local government workers could go on for months, a union warned tonight.
Walkouts lasting a week or more may be on the cards if demands for greater increases are rejected, Northern Ireland Public Service Alliance (NIPSA) deputy general secretary Brian Campfield said.
Picketers from town halls, school canteens and refuse depots across the country began their two-day strike at midnight. Summer schemes were closed and the City of Derry airport shut down.
"I think this very clearly could last months if there's not a resolution," Mr Campfield said. "What would our members think if they went out on strike and there was nothing to show for it?"
Education and library board, housing and council workers all took part in today's action. Up to 500 people attended a rally at Transport House in Belfast this afternoon.
Employers offered a 2.5 per cent pay rise but inflation is at an 11-year high and workers want 6 per cent.
Rising food and fuel costs pushed UK-wide inflation to 3.8 per cent in June from 3.3 per cent in May. That leaves levels well above the government's 2 per cent target.
Employers branded today's action futile and insisted no more money is available.
However, Mr Campfield said indefinite strikes would be considered if other options failed.
"Our members are pressing us to continue the action and NIPSA will be seeking maximum co-operation from all the other unions involved to step up this strike action in the period ahead."
Employers said across the UK, just under a quarter of workers were taking part in the action. But they claimed the figure was lower in Northern Ireland.
Some councils have said their bin collections were unaffected.
Belfast Zoo is closed and the housing executive said it had plans for low staff numbers this week anyway, due to the Twelfth. It is maintaining essential services but offices in west Belfast, Derry and Ballycastle have closed.
Libraries are closed in Belfast, while many are open in the north eastern area.
PA