A Territorial Army soldier who is taking action against his employer after he was made redundant days after returning from Afghanistan "will not be the last", unions have warned.
The Unite union has vowed to fight the decision, warning that it could be in breach of the Reserve Forces Safeguard of Employment Act 1985.
Mike Routledge, a Unite spokesman, said Sunderland would not be the last reservist to take action over being made redundant.
"There are thousands of reservists who have been serving for months overseas, and with nearly a quarter of a million more jobless in the past three months, this will likely not be the only incident," he told Personnel Today.
"Legally, we think this is questionable, but morally, it's utterly unbelievable. I do not know how Cummins had the temerity to make him redundant while he was serving his country."
A spokesman for the American-owned Cummins said: "It is unfortunate that [Sunderland] has been made redundant, but he has not been treated any differently to anybody else. We are very supportive of the British Forces, but when it comes to redundancy we have to follow procedure, which treats everybody the same."
Tim Corry, campaign director of government-run SaBRE (Supporting Britain's Reservists and Employers), warned that employers cut reservists at their own risk.
"There is legislation to try to ensure that both reservists and their employers are treated fairly around a period of mobilisation," he said. "Reservists return from mobilised service with experience in leadership, teamwork and initiative - making them just the kind of employees that employers need in these difficult economic times."