Sanders this month thanked the union’s members “for their support in my campaign.” | AP Photo Pro-Sanders super PAC brought in $2.3 million While the Vermont senator eschews big-money groups, the super PAC affiliated with the nurses union had a record haul.

Bernie Sanders rails against super PACs, but the main super PAC supporting his presidential campaign had its biggest off-year fundraising haul ever, bringing in $2.3 million last year, according to a report filed Sunday morning with the Federal Election Commission.

The super PAC, National Nurses United for Patient Protection, is affiliated with the nation’s largest union of registered nurses, National Nurses United, and its members have been a near-constant presence at Sanders’ rallies.

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National Nurses United for Patient Protection, spent $1.3 million in the second half of the year, including donations totaling nearly $400,000 to a pair of other unlimited-spending groups supporting Sanders ― the California-based Progressive Kick received $245,000 and the Chicago-based Reclaim Chicago got $150,000. Most of the direct spending by National Nurses United for Patient Protection went towards ads, rallies and other voter outreach associated with a bus tour supporting Sanders, according to the report.

Sanders this month thanked the union’s members “for their support in my campaign” and called National Nurses United “one of the sponsors of my campaign and I appreciate that.”

The PAC ended last year with $1.1 million in the bank, though it has continued to spend heavily in support of Sanders’ campaign for the Democratic presidential nomination against Hillary Clinton.

The 2015 fundraising tally of a trio of super PACs supporting her campaign ― $56.3 million ― dwarfed the cash haul of the nurses’ super PAC, almost all of which came after the affiliated union endorsed Sanders for president.

Sanders has continually swiped Clinton as the candidate of big money, including in a statement released Friday a couple hours after the pro-Clinton super PACs announced their huge haul. It boasted that “Bernie Sanders’ raised no money last year for a super PAC.”

Sanders “doesn’t want billionaires’ money. He doesn’t have a super PAC. He believes you can’t fix a rigged economy by taking part in the corrupt campaign finance system in which politicians take unlimited sums of money from Wall Street and other powerful special interests and then pretend it doesn’t influence them,” said spokesman Michael Briggs in the statement.

Clinton's campaign and its supporters have pointed to the nurses’ spending in support of Sanders to suggest his attacks on Clinton as the candidate of big money are disingenuous and hypocritical.

But, according to the super PAC’s FEC filing, almost all of the PAC’s cash flow came in the second half of last year ― and every dime of it came from the union itself. The union did not respond immediately to an email seeking information about its super PAC finances, but the money likely came from dues that members paid to be a part of the union, which come in much smaller increments than the seven-figure checks that fill the coffers of the super PACs that Sanders derides on the campaign trail as eroding American democracy.

For instance, the pro-Clinton super PACs last year accepted $2 million from New York financier George Soros, and $1 million each from Hollywood moguls Steven Spielberg and Jeffrey Katzenberg.