Most of those let go, Weaver said, had been working in Connecticut, Delaware, Maryland, Pennsylvania and Rhode Island, the five states that held primaries Tuesday. Hillary Clinton prevailed in all of those but Rhode Island, tightening her grip on the Democratic nomination.
Weaver said that staffers were informed of the layoffs on Tuesday but that the move had been in the works for some time with the end of the nominating calendar approaching.
"There was never an expectation they would move forward because there's nowhere for them to go," he said. "This is the campaign right-sizing so we can effectively compete in other states."
Weaver said that the dismissed staffers have been given 10 days of severance pay plus any accrued vacation they earned. They will also receive health benefits through May, he said.
The full-time staffers who were laid off all made at least $15 an hour, the figure Sanders has said should be the federal minimum wage within a few years, according to Weaver. He said the campaign has some interns who receive stipends that amount to less than $15 an hour.
Weaver said the campaign has about 60 staffers in California, which offers the largest trove of delegates among the remaining 14 nominating contests.
He said the campaign at one point had more than 1,000 people on the payroll but let many of them go after states with March contests had voted.
Asked if the campaign would be keeping more people on board if Sanders had a more likely path to the nomination, Weaver said it was unlikely that the dismissed staffers would be redeployed to general-election battleground states.
The characterization of "hundreds" of layoffs first came directly from Sanders in a report in the New York Times. Sanders's press staff used the same description throughout the afternoon and evening on Wednesday.
Although Sanders has acknowledged a "narrow" path to the nomination, he has vowed to stay in the race through the convention in July.