Bruce Elmslie, professor of economics, and his co-author Edinaldo Tebaldi, former assistant professor of economics at the University of New Hampshire Whittemore School of Business and Economics, now at Bryant University, said that lesbians, however, do not face similar discrimination in the labour market.
According to the researchers, 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.
Discrimination is most prominent in management and blue-collar, male-dominated occupations such as building and grounds cleaning and maintenance; construction and extraction; and production.
The research team also found that lesbians are not discriminated against when compared with heterosexual women.
They team concluded that while negative attitudes toward lesbians could affect them, lesbians may benefit from the perception that they are more career-focused and less likely to leave the labour market to raise children than heterosexual women.
According to their study, 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 labour force than will a heterosexual woman," the researchers said.
The research team noted that previous studies of attitudes of heterosexual men toward gay men and lesbians show that the bias against gay men is much stronger. Other studies show that gay men are more likely to be the victim of violence because of their sexual identity than lesbians.
The authors referred to a number of possible factors as to why gay men experience labour discrimination and lower wages in certain industries. There is strong evidence indicating discrimination is tied to employer and employee bias.
"Employers may disapprove of gay lifestyles and act on this bias in making hiring decisions," the researchers said.
Employers also may discriminate against gay men in response to the desires of the majority of employees. If employers consider mixing heterosexual and homosexual employees distracting and detrimental to productivity, the researchers said that the employers might consider it profitable to discriminate.
Gay men also may experience labour market discrimination because customers may not want to interact with them, thus influencing hiring practices.
"If customers prefer to interact with heterosexual employees, the owner will act on the customer's taste for discrimination," the researchers said.
The research team said that discrimination might occur as a result of anti-gay attitudes associated with AIDS and misunderstanding as to how HIV is transmitted.
Previous research has shown that people with HIV/AIDS have higher rates of absenteeism from work. The authors theorize that biased employers may be reluctant to hire gay men because they are concerned about a loss of productivity if a worker becomes 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," the researchers said.
In the study, it was found that employee/employer bias was the most prevalent and overwhelming indication of discrimination against gay men.
If the discrimination was consumer-based, the discrimination would be more evident in the services industry where there is direct interaction between employees and customers. If the discrimination was tied to AIDS/HIV status, the distribution of discrimination would be more uniform across industries.
The authors analysed labour and wage information from more than 91,000 heterosexual and homosexual couples collected by the U.S. Census March 2004 Current Population Survey.
The study is published in the Journal of Labour Research.