The boards of a dozen top-300 companies face being dumped by their investors, as protest votes over executive pay double and shareholders put bonuses back in the spotlight ahead of this year's annual meeting season.

The number of top-300 companies to receive a protest vote of 25 per cent or more on executive pay, a "strike" under the controversial "two strikes" rule introduced in 2011 to reign in big pay packets, has doubled from eight to 16 in the first half of 2015, according to research by The Australian Financial Review.