Feb 29 (Reuters) - Institutional Shareholder Services, a proxy advisory firm, on Thursday threw its support behind Starbucks Corp by recommending that investors elect all of management's directors instead of a group of labor unions' nominees.

The Strategic Organizing Center (SOC), a coalition of North American labor unions, last year nominated three director candidates amid an ongoing battle between the coffee chain and its employees over pay, among other things. (Reporting by Svea Herbst-Bayliss; Editing by Leslie Adler)