BERLIN—Tesla’s Berlin factory will elect its first works council on Feb. 28, Germany’s largest union IG Metall said on Thursday, expressing concern that it was too soon for the election to result in a truly representative body. Only one in six of the roughly 12,000 workers expected at the plant have been hired so far, in part because Tesla is still awaiting final approval from local authorities to begin production. The council will consist of 19 members. IG Metall, which represents workers across automotive companies as well as other industrial sectors, fear that calling an election before a wider swathe of workers are hired will lead to a council top-heavy with management. Under German labor law, only employees who have been working at a company for at least six months can stand for election. The results of the election will be valid regardless of what proportion of the workforce votes, …