NEW YORK (Reuters Life!) - Gay men, but not lesbians, face discrimination at work, earning up to 23 percent less than married men in some jobs, according to a new study.

Researchers at the University of New Hampshire (UNH) Whittemore School of Business and Economics spent two years analyzing labor and wage data from 91,000 heterosexual and homosexual couples collected by a 2004 U.S. census.

They found that gay men working in management and blue-collar jobs make less money than straight men due to discrimination by their employers

"It was surprising to see how consistent it was that gay men tended to be more discriminated against in traditionally heterosexual male dominated professions -- blue collar, labor, and management too," researcher Bruce Elmslie, professor of economics at UNH, told Reuters.

The study found that gay men who live together earn 23 percent less than married men, and 9 percent less than unmarried heterosexual men who live with a woman.

They looked at the top 10 occupations that gay men and lesbians tend to be in and found this discrimination showed up most clearly in management and blue-collar, male-dominated occupations such as building and grounds cleaning, maintenance, and construction.

But Elmslie and co-author Edinaldo Tebaldi, who is now at Bryant University in Rhode Island, found that lesbians are not discriminated against when compared with heterosexual women.

He said although negative attitudes toward lesbians could affect them, lesbians may actually benefit from the perception that they are more career-focused and less likely to leave the labor market to raise children than heterosexual women.

According to the study "Sexual Orientation and Labor Market Discrimination," which appears in the Journal of Labor Research, 18.1 percent of lesbians have children, compared with 49.4 percent of straight women.

"Employers could reasonably infer that a lesbian applicant or current employee will have a stronger attachment to the labor force than will a heterosexual woman," said Elmslie.

The researchers cited a number of possible factors as to why gay men faced labor discrimination and lower wages in some industries.

These included employers disapproving of gay lifestyles so not hiring gay men, concern that customers would not want to interact with gay men, and discrimination associated with AIDS and misunderstanding as to how HIV is transmitted or the loss of productivity if a worker became infected with HIV/AIDS.

"If employers perceive one group to be generally less productive or more costly than other groups, individual members of the negatively perceived group will receive lower wage offers regardless of their true characteristics," they said.