Portside

Just two years ago, labor leaders were fretting over the steady erosion of New York City’s reputation as a bastion of unionization. The share of working-age city residents belonging to labor unions was in what they feared was an inexorable decline.

But an annual study scheduled to be released this week suggests that unions may be fighting that trend — if only in New York. The study, conducted by two professors at the City University of New York Graduate Center, found that the proportion of working-age New York City residents who were members of unions had rebounded in the last 18 months to nearly one in four.

“We were surprised, too,” said Ruth Milkman, referring to herself and the co-author of the study, Stephanie Luce. Though the bounce back has been “modest,” they had not foreseen it; two years ago, Professor Milkman was discussing the slide in union membership rates in the present tense and with a tone of inevitability.

On the eve of Labor Day this year, however, she said the share of city residents who identified themselves as union members, a proportion that had fallen to slightly more than one in five, had risen since the start of 2013. The primary cause of the reversal appeared to be a surge in hiring in construction and the hotel industry, not the well-publicized campaigns for higher pay and better benefits by fast-food workers and others earning low wages.

“We don’t see any evidence of that — the fast-food thing,” Professor Milkman said. “While that’s a very visible campaign, they have yet to organize.”

Rather than a result of efforts to organize employees of restaurants and retail chains, Professor Milkman said, the “pretty healthy uptick” in union membership among New Yorkers appears to be a function of rising employment in industries with traditions of strong unions, such as construction. In an interview, she cited surveys by the federal government that pointed to significant increases in iron workers, plumbers, pipe fitters and other building trades that are highly unionized in New York.

Despite reports of a growing number of construction projects in the city opting for less costly, nonunion labor, Professor Milkman said the number of union jobs was probably growing at the same time.

“The same thing is happening in the hotel industry,” she said. “There are more nonunion hotels, too, but employment in the hotel industry is growing even faster.” She said it was “too soon to know” if the turnaround would continue or subside. But she added, “There was a long-term decline in the private-sector union density, and now it seems to have reversed.”

Ed Ott, a former director of the New York City Central Labor Council, an umbrella organization of unions with over one million members, said he was not prepared to call the turnaround a trend. But Mr. Ott added, “If it is a trend, it’s definitely a positive sign.” He said that in part, it reflected an effort by building trades’ unions “to win back market share” from nonunion workers.

New York City and the rest of the state already stood out for their high unionization rates. About 24 percent of city residents and 25 percent of state residents are union members, more than double the 11 percent rate for the country as a whole, according to the study, titled “The State of the Unions 2014.”

Professor Milkman and Professor Luce are affiliated with the Joseph S. Murphy Institute for Worker Education and Labor Studies at CUNY.