June 6 (Reuters) - Proxy advisory firm ISS on Friday

urged shareholders of casino operator Penn Entertainment ( PENN )

to elect all three nominees of hedge fund HG Vora to

its board ahead of its June 17 annual meeting.

"The company is facing sustained challenges, which have

resulted in total shareholder return and operational

underperformance," ISS said in a note.

Penn did not immediately respond to a request for comment.

HG Vora said in April that it planned to push ahead with a

proxy fight at Penn to try and elect all three of its director

candidates after the casino operator said it would appoint only

two of them to its board.