For some New York-based employees who lost their jobs last week, the news came immediately after the campaign had circulated an email informing them that a coworker was infected with the coronavirus and they had potentially been exposed.

Mr. Bloomberg — a multibillionaire who entered the Democratic race in late November and dropped out in early March — assembled an army of campaign workers quickly, attracting them with unusually high pay, full benefits and the lure of campaign work through the fall, regardless of who won the Democratic nomination. He spent more than $900 million along the way and repeatedly promised to deploy his campaign in service of whoever the party ultimately selected.

But on March 9, days after he exited the race, Mr. Bloomberg’s campaign laid off field workers in all but six battleground states, asking if they were open to relocating to one of those states — Arizona, Florida, Michigan, North Carolina, Pennsylvania and Wisconsin — or if they wanted to be referred to another presidential campaign.

Last week, as he announced an $18 million donation to the Democratic National Committee in place of a new super PAC designed to help Democrats in the presidential race, Mr. Bloomberg also laid off staff members like Ms. Wood who had worked in those six states.

His campaign invited all former employees to apply to work for the D.N.C., though it called the hiring process competitive and specified that pay and benefits would be different. The campaign said in a news release last week that D.N.C. staffing would draw “in part from our own incredibly experienced and talented organizing staff.”

Some affected employees, including people who had left stable jobs to work for Mr. Bloomberg, as Ms. Wood did, expressed frustration publicly, in spite of the confidentiality and non-disparagement agreements they had signed. They said they would not have accepted the work had they known its true terms.

Most immediately, some former employees, like those from Georgia, Utah and Washington who sued on Monday, were seeking to be freed from those broad confidentiality agreements, according to Peter Romer-Friedman, a lawyer at the firm Gupta Wessler who represents them.