Sen. Bernie Sanders frequently attacks Amazon on the campaign trail, vowing to break up the online retail giant if elected, denouncing its treatment of workers and decrying its ability to pay no federal taxes on billions in profits.

That’s why impassioned dissent erupted within the Sanders campaign earlier this year over its purchases of large amounts of supplies through Amazon, according to five people with knowledge of the situation. Carli Stevenson, then a senior Sanders campaign aide in New Hampshire, raised concerns directly with national campaign officials and suggested using a different company, three of the people said.

Another New Hampshire staffer, state political director William Bateson, also voiced opposition to using Amazon, according to two of the people with knowledge of the situation. Stevenson and Bateson declined to comment for this story.

The Sanders campaign continued using Amazon despite the concerns. Through September, it had spent more than $233,000 on Amazon purchases — much of it in office supplies, and often through Amazon’s Marketplace feature — a review of campaign finance records shows.

The Washington Post is owned by Jeff Bezos, Amazon’s founder and chief executive, but the newsroom staff operates with independence in its coverage.

The campaign’s spending on Amazon is a small fraction of the more than $40 million it shelled out on operating expenditures during the same period. But it was more than other campaigns spent on the company, and more than enough to prompt surprise and complaints from staffers who felt it conflicted with the campaign’s principles.

These internal protests drew a response from a senior Sanders campaign official, who said the alternatives to Amazon also had ethical issues.

“I hear you on amazon but who is the paragon of virtue in . . . office supplies?” wrote senior Sanders adviser Jeff Weaver in an email over the summer, according to a person who saw the email and described it to The Washington Post. “I hear uline is terrible. Cant beleive staples is a great company but happy to shown I’m wrong.”

Uline, a packing supplies company, was founded by Dick and Liz Uihlein, who are top Republican donors. The private equity firm Sycamore Partners bought Staples in 2017.

Weaver did not respond to multiple requests for comment. The people with knowledge of the internal situation spoke on the condition of anonymity out of fear of retribution.

An Amazon representative declined to comment on Sanders’s remarks about the company, pointing to tweets the company previously issued defending its tax structure and highlighting a worker training program.

In a statement, Sanders campaign spokesman Mike Casca said, “We agree that too few companies have too much power over our economy and our media in America and they often don’t pay their fair share of taxes, which is why a Sanders administration will take them on.”

He declined to answer questions on why the campaign opted to use Amazon, whether Sanders (I-Vt.) was aware of the campaign’s purchasing practices and whether it was still using the retailer.

The Amazon purchases are not the campaign’s only business practice to spark internal protest. In April, the campaign used Airbnb to arrange housing for state staff who traveled to Washington for a team meeting, triggering blowback from New Hampshire campaign staffers reluctant to use the company, according to three people with knowledge of the situation. Critics of Airbnb have argued it negatively impacts housing prices and hotel workers.

These internal disputes, which have not been previously reported, underline a basic tension in the Sanders campaign: Many employees see it as not just a bid for office but a social movement that stands for workers’ rights and reining in big corporations. Some have privately vented that the campaign doesn’t always live up to those ideals.

That tension was also evident over the summer during a standoff between management and unionized Sanders field staffers over pay, with some employees complaining that their salaries conflicted with the senator’s calls for a minimum wage of $15 an hour. After the dispute became public, the workers won a raise.

At the same time, the Sanders campaign has won plaudits from liberal activists for practicing its principles in other ways, such as committing to offset all carbon emissions produced from campaign travel by partnering with an emissions reduction project; being the first presidential campaign to unionize its workers; and striving to stay in unionized hotels.

The Sanders campaign spent the vast majority of its Amazon investment on Marketplace, a section on the company’s website where third-party sellers offer their products. More than 50 percent of Amazon’s total unit sales come from third-party purchases, according to the company, and Amazon collects fees from the sellers.

The Sanders campaign also bought office supplies from other sources, though to a much lesser degree — spending nearly $82,000 total at retailers including Staples, Apple, Target, Office Depot and Walmart, campaign finance records show.

Stevenson, who initially served as deputy state director and communications director in New Hampshire for the campaign and is now a state coordinator in Indiana, recommended to national campaign officials that they discontinue using Amazon and buy from a company more in line with the campaign’s values, according to three people with knowledge of with situation. She suggested using a company called the Green Office instead.

That company, which has operated on a much smaller scale than Amazon, bills itself as a “one-stop online retailer featuring over 60,000 green and conventional office products.” Much of its inventory was out of stock this past week, a review of the website showed, and the phone number listed on the website was out of service.

Some of the campaign’s most vocal internal protests came from staffers in the New Hampshire office, but at least a handful of staffers in other parts of the campaign also felt the use of Amazon clashed with Sanders’s rhetoric, people with knowledge of the situation said.

Sanders has long been an outspoken critic of Amazon’s leadership. Appearing at a Washington Post Live event in July, Sanders said: “Amazon last year made over $10 billion in profit. What do they pay in taxes? Not a nickel in federal income taxes. Does anyone think that that is vaguely sane?” That echoed a common refrain on the campaign trail.

In August, Sanders took aim at The Post, accusing the newspaper of being biased against his campaign due to his criticism of Amazon. He later clarified to CNN that he did not think Bezos was instructing the editor of The Post on the newspaper’s coverage.

“But what I think is, in media in general, there is a framework,” Sanders said, that does not prioritize questions about income and health-care inequality.

Sanders also voiced support for striking Amazon workers on “Prime Day,” a major annual sale day for the retailer. “I stand in solidarity with the courageous Amazon workers engaging in a work stoppage against unconscionable working conditions in their warehouses,” Sanders tweeted in July.

An analysis by Bloomberg News found that the Sanders campaign spent more than its Democratic rivals on Amazon through the end of September, when the latest finance reports were available. Sen. Elizabeth Warren (D-Mass.), who has also been a staunch Amazon critic, was the second-biggest spender, the analysis showed. Sanders and Warren have brought in more money than their rivals, however, giving them more to spend.

Another point of contention inside the Sanders campaign was the use of Airbnb for a campaign meeting in April, a busy time for visiting the nation’s capital. The campaign’s expenditures on Airbnb are a very small portion of its overall spending on lodging.

Still, campaign workers from New Hampshire, including Stevenson and then-senior adviser Kurt Ehrenberg, were not pleased about the use of Airbnb, according to three people with knowledge of the situation. Then-state director Joe Caiazzo brought the complaints to national campaign personnel, two people with knowledge of the situation said. An Airbnb spokesman defended its business practices.

Ehrenberg and Caiazzo had also expressed concerns about using Amazon, people with knowledge of the situation said. Both men are no longer with the Sanders campaign. Both declined to comment.

At a culinary workers union meeting in Las Vegas this month, Sanders was asked about Airbnb by a woman who said she saw problems associated with the company as an issue for workers like her. “How are you going to stop this?” she asked.

“There are a lot of issues involved,” Sanders replied. “And the answer is we’re going to look very, very thoroughly at that.” He added, “We will stand with you in any and every way. We will take a very hard look at the impact of these B&Bs on the industry.”