A study released on Friday, noting the gains made by black union workers in New York City, said that raising the rate of unionization among black workers across the country would help narrow the racial pay gap.

The study, conducted by two professors affiliated with the Murphy Institute for Worker Education and Labor Studies at the City University of New York, which issued the report, described high unionization rates for black workers who live in the city compared with national rates.

Nearly 40 percent of black workers who are city residents are union members, compared with roughly 13 percent of black workers nationally.

The difference between the rates of black and nonblack unionization is also especially pronounced in New York City. The black unionization rate is nearly double that of nonblacks in the city, a difference that is much smaller nationally.