Italian energy group Eni said two people had been killed in an accident at a Sicilian plant operated by its Versalis chemical unit, prompting trade union calls for a strike to protest over working conditions. The two workers, employed by a third-party contractor, had been carrying out inspection work at the Versalis ethylene plant in Priolo on the southeast of the island. The causes of the incident were still under investigation, the company said on Wednesday, adding that it considered the safety of its employees and contractors to be of the utmost importance. Italy's three largest trades unions have called for a strike on Thursday at the Priolo industrial area, a union official told Reuters. "Unfortunately in Italy contractors are considered second-class workers with few rights and safeguards," said Enrico Miceli, general secretary of trade union Filctem-Cgil . Versalis, wholly owned by Eni, is Italy's largest Italian chemical company by sales, production volumes and number of employees.