Protests have been held outside offices of Sinn Féin and the Democratic Unionist party over the two parties’ decision to accept welfare reforms imposed by London to prevent the collapse of power sharing in Northern Ireland.

The protests, organised by an affiliate of the Unite union, took place in Belfast, Newry and Ballymoney. Unite is also demonstrating against the DUP and Sinn Féin’s backing for a lower corporation tax regime in Northern Ireland, which the union claims will be paid for with hundreds of millions of pounds of cuts to local public services.

Fifty union activists protested outside the Sinn Féin office on Belfast’s Falls Road, and another 50 took part in a demonstration at the DUP’s constituency advice centre across the peace line on the loyalist Shankill Road. Smaller groups protested in Newry and Ballymoney, and another protest was to be held in Derry on Saturday afternoon.

The protests will be particularly embarrassing for Sinn Féin. In the Irish Republic, the party has been campaigning on an anti-austerity programme and hopes to gain power in a coalition after the general election, which is expected in late February or early March.

Far-left parties such as People Before Profit have accused Sinn Féin of double standards by allowing Tory-inspired cuts to public services in Northern Ireland while opposing austerity in the republic.

Albert Hewitt, the Unite Community organiser in Northern Ireland, said the deal to save the Stormont government would result in devastating cuts to social welfare as the price David Cameron and George Osborne extracted for allowing the power-sharing executive led by Sinn Féin and the DUP to set a low corporation tax.

“Perhaps of greatest concern is the deal’s proposal to reduce corporation tax to 12.5% in an unwinnable race to the bottom on global tax-haven status,” Hewitt said. “No one knows just how much this will cost but we can be certain that this will mean hundreds of millions of pounds of further cuts to public expenditure budgets at a time when we cannot afford them.

“Our communities deserve better. These protests send a clear signal that Unite in the community will be at the forefront of the campaigning against austerity in Northern Ireland.”

Erik Cownie, the west Belfast chairman of Unite Community, said: “Working class people are fed up with cuts and they are fed up with the politics of just orange and green. This is unprecedented and is a nascent movement.”

Unite Community is affiliated to the Unite union and is an alliance of community organisations, students and pensioners’ rights groups across Northern Ireland.