The cash-and-stock-deal, first announced in November, has become one of the year's most contested, with large Ritchie Bros investors announcing their support and opposition to the plan.

Hedge fund Luxor Capital, which owns roughly 4.2% of Ritchie Bros, has been urging other shareholders to vote against the deal. The fund argued the deal is risky and would distract Ritchie Bros, which auctions used heavy equipment and trucks, from its core business and hurt shareholders.

IAA's stock price jumped 10% on the news of a majority of Ritchie Bros investors voting for the deal.

Spokespeople for Ritchie Bros and IAA did not immediately respond to requests for comment.

Earlier this week, proxy advisory firms Institutional Shareholder Services and Glass Lewis recommended Ritchie Bros shareholders vote against the takeover. Smaller proxy adviser Egan-Jones recommended shareholders vote for it.

Ritchie Bros has argued the acquisition would unlock substantial value that neither Ritchie Bros nor IAA could achieve alone.

(Reporting by Svea Herbst-Bayliss in Rhode Island; editing by Grant McCool)

By Svea Herbst-Bayliss