Vermont Sen. Bernie Sanders is concerned that supporters aren't donating enough money, according to a new email sent from his campaign Tuesday afternoon.

"The bad news is, our average donation amount is far less than anyone else. This month our average donation is lower than it’s ever been — right around $14," the socialist 2020 candidate wrote. "That means it takes 200 donations to match 1 max-out check being scooped up at a swanky fundraiser held by one of our opponents."

Sanders has long championed his average campaign donations as proof of his authenticity and that he doesn't need to rely on wealthy donors to fund a White House run. During his last presidential campaign in 2016, Sanders' average donation was $27.

"We need people to give just a bit more than they have before," the campaign said. "Right now, most first-time donors are giving three dollars. If you could possibly chip in $10, we’d be back on track to hold our fundraising advantage. And that’s important, because if we do, we’ll win. What do you say?"

Sanders is neck and neck with former Vice President Joe Biden in polls for the Democratic nomination. Sanders' campaign has raised more than $18 million since he announced his candidacy on Feb. 19.