WASHINGTON (Reuters) – The U.S. Department of Labor on Tuesday unveiled a proposal that would make it harder for companies to treat workers as independent contractors, potentially upending the gig economy and other industries that rely heavily on contract labor, the latest effort by the Biden administration to reverse a Trump-era rule. Legal battles over which workers can be classified as employees, which forces companies to pay overtime and foot the bill for payroll taxes, social security and benefits, have raged since companies like Uber, Doordash and Lyft have become popular in the United S…