Despite their qualifications and experience, these job seekers contend that they have not been given a fair shot because of one counterintuitive reason: They are already unemployed.

“I’ll do anything — but somebody has to be willing to hire me,” said Mr. Mango, 43, who has not worked in nine months and said he lost his home because he could not pay the rent. “If you’re not working, that’s already Strike 1 against you.”

New York City appears likely to adopt a law that would allow unsuccessful job applicants to sue businesses who they believe hold their unemployment status against them in making hiring decisions. The measure is widely seen as the toughest step yet in a flurry of recent efforts by the Obama administration and elected officials in at least 18 states, including New York, to help the long-term unemployed.

The District of Columbia passed a law last year that made it illegal for employers to refuse to consider or hire candidates because they were out of work, and barred advertisements from suggesting that the unemployed need not apply. Laws prohibiting discrimination in job listings have also been adopted by New Jersey and Oregon; a similar measure in California was vetoed by the governor.

Though businesses are reluctant to acknowledge bias in their hiring practices, some human-resource managers and consultants say privately that unemployment can be a red flag on a résumé, signaling that a worker may have outdated skills, or may be a short-timer who is desperate enough to take any work now but will leave when something better comes along. The National Employment Law Project, a nonprofit advocacy group, reported that companies across the country often posted job notices explicitly excluding applicants who are unemployed.