(Adds details on Iger compensation, comments from proxy adviser)

By Lisa Richwine

March 8 (Reuters) - Walt Disney Co shareholders rejected an executive compensation plan that could reward Chief Executive Officer Bob Iger with up to $48.5 million a year over four years plus an equity grant worth about $100 million, in a non-binding vote on Thursday.

The total compensation is tied to the closing of Disney's planned $52.4 billion acquisition of film and TV assets from Twenty-First Century Fox and meeting performance targets.

Fifty-two percent of shareholders voted against Disney's compensation plan for Iger and other executives, the company said at its annual shareholder meeting in Houston. Forty-four percent cast ballots in favor and 4 percent abstained.

"The board accepts the result of today's non-binding vote and will take it under advisement for future CEO compensation," Aylwin Lewis, chair of the board's compensation committee, said in a statement.

Iger's continuation as chief executive is imperative in light of the planned Fox acquisition, Lewis said, noting that total shareholder return has more than quadrupled over Iger's tenure.

Iger has been CEO since 2005 and added the title of chairman in 2012.

Under the compensation plan, Iger would be paid up to $48.5 million in annual salary and bonuses if the Fox deal goes through, for each of the four years from 2018 to 2021.

Iger was also awarded an equity grant that could be worth about $100 million in 2021, according to proxy adviser Institutional Shareholder Services, which urged investors to vote against the pay resolution. Seventy-five percent of the grant is based on Disney's total shareholder returns compared with the S&P 500 Index.

Iger's compensation reached $36.3 million in fiscal 2017. His contract was extended through 2021 when Disney announced the Fox deal in December.

It is unusual for shareholders to vote against executive compensation. Just 1.2 percent of S&P 500 companies failed to win majority support for their advisory pay resolutions in 2017, according to ISS Analytics.

ISS said the "substantial" payments to Iger tied to the Fox merger were "concerning."

"While we acknowledge the need to retain critical leadership in anticipation of such a significant merger, the magnitude of the special equity grant ($100 million) is excessive," ISS said in a January report.

Lewis said the board had decided it was "imperative" for Iger to remain to oversee the integration of Fox businesses and that Fox also felt his continued leadership was "essential."

Total shareholder return has jumped 414 percent during Iger's tenure, and Disney's market capitalization has climbed to $156 billion from $46 billion, Lewis added.