His labor-policy plan could have come from Sanders or Warren.

Mike Bloomberg pitches himself as a moderate, business-minded alternative to other Democrats running for president. But his plan to remake the nation’s labor laws, released earlier this month, wouldn’t be out of place in the campaign literature of Bernie Sanders or Elizabeth Warren.

Start with Mr. Bloomberg’s endorsement of a $15 minimum wage, which has already hurt the restaurant industry in the city he once led. Quick-service restaurant employment growth in New York City averaged 7% between 2010 and 2015, according to data from the state Labor Department; in 2018 and 2019, it was less than half that. In the full-service restaurant industry, the city has lost jobs for the past two years, something that hasn’t happened since the early 1990s. If $15 is bad for workers in Midtown Manhattan, imagine the consequences in Manhattan, Kan.

Mr. Bloomberg used to appreciate that reality. In 2009 a proposed $11.50 “living wage” requirement for commercial tenants killed a 2,200-job development for the vacant Kingsbridge Armory in the Bronx. Mr. Bloomberg said the outcome “couldn’t be worse.” The city’s Economic Development Corp. later released a 350-page report by outside consultants on the harm of living-wage requirements. The mayor even sued to invalidate a living-wage law after the City Council overrode his veto.

What happened to that Mike Bloomberg? His new labor plan reads like a union leader’s wish list. He would ban right-to-work laws, forcing employees in 27 states to pay dues to a labor organization as a condition of employment. He would try to skirt the Supreme Court’s 2018 Janus decision and ensure that “public-sector unions have maximum flexibility to collect revenue.” He would follow California in undercutting the many workers who choose to be independent contractors. He backs mandatory “card check” recognition that effectively eliminates an important democratic norm—the secret ballot—from a vote on whether to unionize. Under Mr. Bloomberg’s plan, employers would be prohibited from requiring employees to attend an informational meeting before a union vote.

These proposals are radical even for Democrats. A national “card check” proposal died in the Democrat-controlled Senate in 2009. (In a 2008 op-ed on these pages, George McGovern called card check a “disturbing and undemocratic overreach.”) More recently, Democratic legislators in Virginia backed off a proposal to eliminate that state’s right-to-work law after realizing that it would harm the state economy.

As mayor, Mr. Bloomberg had a frosty relationship with the city’s unions. Stuart Appelbaum, president of the Retail, Wholesale and Department Store Union, accused him of “turning a blind eye to the plight and reality of some of our city’s hardest-working residents.” The mayor’s support of merit pay for teachers led to repeated clashes with the United Federation of Teachers. Mr. Bloomberg seems determined to atone for his past—and workers will pay for it.