Donald Trump ally Roger Stone called on delegates to formally pledge to support the billionaire at the Republican National Convention past a first ballot, warning of a vast “big steal” effort underway to block Trump from the nomination.

In a column for Breitbart, Stone suggested certain “Trojan horse” Trump delegates were “inserted as quislings by the party bosses” to vote against Trump on a possible second ballot at the summer convention.

“The big steal happens even if Donald Trump hits the magic 1237!” Stone wrote. “The fix is in. The same insiders who have nearly destroyed the Republican Party are at it again, plotting in a backroom deal to block Donald Trump’s nomination as the GOP candidate for President.”

Stone also claimed his earlier threat to disclose the hotel room numbers of delegates “involved in the steal” were misconstrued by the media and violence “would be counterproductive to Trump’s general election drive.”

Sen. Ted Cruz’s (R-TX) campaign is hard at work trying to “chisel” delegates away from Trump in states where the real estate mogul won, according to Stone, citing Louisiana and Arkansas as examples.

Signing onto the voluntary pledge would also let voters know who they could trust, Stone wrote.

Stone’s remarks come as delegates around the country, who are usually low-level local party officials, have begun receiving death threats and intimidation they say comes from pro-Trump forces.

Tension around delegate selection is higher than usual as Trump’s hopes of arriving at the summer convention with the delegates needed to win the nomination outright have dimmed.