Shadow health secretary Andy Burnham said he wanted reassurances that that a Government-backed inquiry into the conduct of industrial disputes was not a "political call".
"Of course if there's been intimidation it's unacceptable and that should apply to unions as well as employers," he told BBC One's Sunday Politics show.
"I think I need reassurance that this isn't a political call by Mr Cameron designed to report near the election, so you know we'll see how this develops."
More top news
Ross and Brad Naylor have spoken about learning their father had died in the Tunisia attack and the struggle coming to terms with his death.
Tony and Christine Callaghan, who were both injured in the attack, said they were angered to learn of the slow response by security forces.
Police offer £50,000 reward for information on a fire in Chinatown that killed homeless men.