(CNN) Rep. Alexandria Ocasio-Cortez of New York and Rep. Ilhan Omar of Minnesota are endorsing Sen. Bernie Sanders for president, several sources told CNN.

Fellow "squad" member Michigan Rep. Rashida Tlaib is also expected to back the Vermont independent, according to a source familiar with the process, but Tlaib said in a statement Wednesday morning, "I have not made any endorsement at this time."

She will, however, welcome Sanders to her district on October 27, Tlaib and the Sanders campaign said.

"I need to know that anyone I choose to endorse will fight for my residents," Tlaib said, "and I appreciate the opportunity for them to have a dialogue with Senator Sanders about these critically important issues."

The backing of Ocasio-Cortez, who is expected to formally announce her endorsement at a Sanders rally Saturday in New York City, and Omar on Tuesday night was a welcome boost for the Sanders campaign, which has gone to great lengths to win over voters of color and create the kind of diverse coalition that mostly eluded it in 2016. Whether their support will sway progressive voters, who according to recent polls have been drifting toward Sen. Elizabeth Warren of Massachusetts, is less clear.

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