DNA tests can reveal predisposition to a wide range of diseases
The United States Senate has unanimously passed legislation banning discrimination on the basis of people's genetic details.
The proposal, which passed 95-0, still needs approval from the House of Representatives before it becomes law.
It would allow only patients and their doctors to access data obtained through genetic testing.
Employers, unions and health insurance companies would be forbidden from discrimination via genetic information.
The Democratic Senator Edward Kennedy called it the "the first new civil rights bill of the new century".
He added: "Discrimination based on a person's genetic identity is just as unacceptable as discrimination on the basis of race or religion."
The bill would forbid health insurers from refusing coverage, or raising premiums, for healthy people based on genetic information.
Insurers would also not be allowed to require people to take tests which might show a predisposition to a disease.
And employers would be prohibited from using genetic information in decisions over hiring, firing, promoting or compensating employees.
The bill is supported by the White House and by health insurers, but opposed by some business interests, including the US Chamber of Commerce.
Scientists hope the legislation will encourage more people to come forward and take genetic tests that might save their lives.
Such tests can lead to therapy for a wide range of diseases with hereditary links, such as cancer, diabetes and heart disease.
With the mapping of the human genome in 2003, far more information is available about people's disposition to illnesses.
The Republican sponsor of the bill, Senator Olympia Snowe, said that for the first time steps were being taken "to prevent discrimination before it has taken hold".
"That's why this legislation is unique and groundbreaking," she added.
The genetic tests currently available were "absolutely useless", she said, if people were not taking them for fear of discrimination.
Employers had previously expressed concern that a bill of this kind would lead to inappropriate claims, but one consolation for insurance companies is that they will still be able to charge higher premiums if someone is already ill when they apply for cover.
The vote in the House of Representatives is expected early next week, after which the bill will go to President George W Bush to be signed into law.