Story highlights A super PAC tied to a union supporting Bernie Sanders has spent almost $570,000 to help the Vermont senator

Sanders has repeatedly criticized super PACs and called for campaign finance reform

Washington (CNN) A super PAC tied to a union supporting Bernie Sanders has spent almost $570,000 to help his presidential run, according the Sunlight Foundation and representatives from the group, spending that contradicts some of what the Vermont senator has said in the past about campaign finance reform.

National Nurses United For Patient Protection, a independent expenditure group, or super PAC, has spent $569,000 backing Sanders. National Nurses United, the union associated with the group, endorsed Sanders in August , the first national union to do so, and has since been seen supporting him at events across the country.

The backing offers proof that it will be difficult for Sanders to stick to a no-super PAC pledge.

One of the most well-received lines in Sanders' stump speech is when he blasts super PACs and suggests that they have a corrupting influence on the political system. Many of his supporters say one reason they like him is because of his view on super PACs, which are not subject to campaign finance limits.

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