White House contender Bernie Sanders got back on message at Pennsylvania's AFL-CIO convention on Thursday, trumpeting his platform of Medicare-for-All, free higher education, and a $15 minimum wage to a reportedly receptive audience of organized workers and their families.

"I believe that we need to pass legislation that will make it easier, not harder, to join labor unions," he said.

His speech, however, was not barb-free, zeroing in on the candidates' different approaches to campaigning.

"I will not leave here this morning and go to a Wall Street fundraiser," Sanders told the crowd gathered in Philadelphia, which applauded. "I will not be—I will not be hustling money from the wealthy and the powerful. I grew up, in a sense, in this movement. You are my family. And we will win or lose this campaign on the backs of working families."

His rival Hillary Clinton has drawn fire for hopping on and off the campaign trail to raise money with, and from, high-powered lobbyists and Wall Street elite.

Just this week, Intercept reporter Zaid Jilani wrote: "As Hillary Clinton questions rival Bernie Sanders over the depth of his financial reform ideas this week, a group of former government officials—once tasked with regulating Wall Street and now working in the financial industry or as Wall Street lobbyists—are participating in a fundraiser for her in the nation's capital."

Politico reports that Sanders also pointed to the fact that he is the only candidate without a super PAC, "because I do not want or need the money from Wall Street or the drug companies or the other powerful special interests who already have so much influence over what goes in Washington."

In recent weeks, the contrasts between the Democratic candidates' fundraising machines have become increasingly apparent. Whereas Clinton has leaned on big-ticket fundraisers and super PAC donations, the bulk of Sanders' donations have come in the form of small, individual donations.

"We have received over six million individual campaign contributions averaging 27 dollars apiece—I believe that is the future of the Democratic Party," Sanders told attendees at the Wisconsin Democratic Founders Day Gala at Wisconsin Center in Milwaukee last week.

Meanwhile, a Center for Public Integrity (CPI) investigation, published Thursday, reveals that when it comes to campaign finance, "Clinton's own election efforts are largely immune from her reformist platform."

"Clinton's massive campaign machine," writes CPI senior reporter Dave Levinthal, "is built of the very stuff—super PACs, secret cash, unlimited contributions—she says she'll attack upon winning the White House."