However, Labour MP Paul Flynn said the Government had left the agency “emaciated” and said that the Conservatives were “hypocrites” for blaming staff.
Mark Serwotka, general secretary of the union, blamed the Home Office for the strike because working conditions had become “intolerable”.
“It’s a strike that’s been brought about because we have an agency in crisis,” he told BBC radio. “The agency is trying to muddle its way through and the public deserve better.
“But we’re also saying that our members deserve better because the stressful conditions that civil servants are working in are intolerable. There’s a long hours working culture, people are under real pressure to meet targets with diminishing resources. The answer is obvious — we need more staff.”
Last month, Home Secretary Theresa May apologised to people affected by delays because the forecast for applications had been “substantially exceeded” and extra staff were drafted in to deal with the backlog.
