Sen. Bernie Sanders' attacks against Walmart may be helping fundraising efforts for his presidential campaign.

Sanders' campaign said Tuesday that it raised $18 million during the second fundraising quarter of the year, and that Walmart was the top employer of his donors for the period.

Other leading employers of Sanders' donors included Amazon, Starbucks, Target, and the US Postal Service. More than 99% of donations were $100 or less, according to the campaign.

Sanders' campaign said the data indicates that support for the Vermont senator — who has been an outspoken critic of Walmart, Amazon, and other large corporations — is coming from "working people."

"While other candidates court big money at fancy fundraisers, this campaign is supported by teachers, retail workers, and nurses who are putting what little money they have behind the one candidate who can bring about the transformative change this country needs," Sanders' campaign manager Faiz Shakir said in a statement.

It's also possible that these statistics are simply a reflection of the general US population, as Walmart and Amazon are the top private employers in the US.

Read more: Bernie Sanders accuses Walmart of paying 'starvation wages,' attacks the CEO's pay, and praises Amazon

Sanders has called on Walmart to raise its starting wages to $15 per hour. He attended Walmart's annual shareholders' meeting in June and accused the company of paying "starvation wages " that "are so low that many of these employees are forced to rely on government programs like food stamps, Medicaid, and public housing in order to survive."

He also attacked Walmart CEO Doug McMillon's compensation, which reached nearly $24 million last year.

"Frankly, the American people are sick and tired of subsidizing the greed of some of the largest and most profitable corporations in this country," Sanders said at the meeting.

Walmart last year raised its starting wages to $11 an hour.