SAN FRANCISCO, July 18 (Reuters) - Proxy advisory firm Institutional Shareholder Services (ISS) on Monday recommended Tesla Inc investors vote against the re-election of two of its board members, Ira Ehrenpreis and Kathleen Wilson-Thompson.

ISS cited concerns about "the board's risk oversight in light of the pledging (as collateral) of a significant amount of the company's stock by certain directors" as one of the reasons for the recommendation.

ISS also urged Tesla investors to vote for a shareholder proposal regarding the right of employees to form a labor union. (Reporting by Hyunjoo Jin; Editing by Christopher Cushing)