(CNN) Three progressive House Democrats who won their seats by challenging Democratic incumbents are rebuking a new rule by the Democratic Congressional Campaign Committee that prohibits the organization from conducting business with "political vendors" that support primary challengers to incumbents, calling the rule a "blacklist" that weakens the party.

Reps. Alexandria Ocasio-Cortez of New York, Ayanna Pressley of Massachusetts and Ro Khanna of California have called out the DCCC for the new rule, which is included on a form for vendors looking to partner with the organization.

"The core mission of the DCCC is electing House Democrats, which includes supporting and protecting incumbents," the form read. "To that end, the DCCC will not conduct business with, nor recommend to any of its targeted campaigns, any consultant that works with an opponent of a sitting Member of the House Democratic Caucus."

On Saturday, Ocasio-Cortez, who defeated former Rep. Joe Crowley last summer in the party's primary, cast the rule as a "blacklist" and a "boycott," writing in a tweet that it's "extremely divisive & harmful to the party."

The freshman congresswoman, who amassed a national following of supporters after her two wins last year, called for "small-dollar" donors to stop giving their donations to the DCCC and instead give them directly to "swing candidates." She went on to name a few campaigns that she said should directly receive donations.

The @DCCC's new rule to blacklist+boycott anyone who does business w/ primary challengers is extremely divisive & harmful to the party.



My recommendation, if you're a small-dollar donor: pause your donations to DCCC & give directly to swing candidates instead.



Some great ones: — Alexandria Ocasio-Cortez (@AOC) March 30, 2019

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