Halliburton and Baker Hughes are preparing to call off their $28bn (£19.2bn) merger, which has met stiff antitrust resistance from regulators in the US and Europe, a person familiar with the situation said. The companies, the second- and third-largest oil-service firms, could announce as soon as Monday morning that they have terminated the combination, according to Bloomberg. The companies had set a deadline for the end of April to complete the deal or walk away. If the merger collapses, Halliburton will have to pay Baker Hughes a $3.5bn termination fee.