Dozens of Republican convention delegates are hatching a new plan to block Donald Trump at this summer’s party meetings, in what has become the most organized effort so far to stop the businessman from becoming the GOP presidential nominee.

The moves come amid declining poll numbers for Trump and growing concern among Republicans that he is squandering his chance to defeat Democrat Hillary Clinton. Several controversies — including his racial attacks on a federal judge, his renewed call to temporarily ban Muslims from entering the United States and his support for changing the nation’s gun laws — have raised fears among Republicans that Trump is not really a conservative and is too reckless to run a successful race.

Given the strife, a growing group of anti-Trump delegates is convinced that enough like-minded Republicans will band together in the next month to change party rules and allow delegates to vote for whomever they want at the convention, regardless of who won state caucuses or primaries.

The new push is being run by people who can actually make changes to party rules, rather than by pundits and media figures who have been pining for a Trump alternative. Many of the delegates involved supported Sen. Ted Cruz (Tex.) in the primary race but say they are not taking cues from any of Trump’s vanquished opponents.