Atlanta (CNN) Progressive activist groups backing Keith Ellison in the race to chair the Democratic National Committee are making a final push for the Minnesota congressman the day before the vote.

In a letter to DNC members obtained by CNN, the leaders of five groups at the heart of the political left -- MoveOn, the Progressive Change Campaign Committee, Democracy for America, 350 Action and Presente Action -- argued that only Ellison can bridge the divide between the Democratic establishment and the party's grassroots.

The groups also said they'd be "eager to engage" directly with the party's infrastructure under Ellison's leadership.

It was an implicit rebuke of former Labor Secretary Tom Perez, who is in a tight race with Ellison for DNC chair.

The letter comes as progressive groups -- many of which allied with Bernie Sanders during the 2016 Democratic presidential primary -- make their final case for Ellison even as Perez's camp says it is near the 222 of 442 eligible voting DNC members it will need to secure the job.

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