Bank of America will soon reimburse gay employees who insure same-sex partners for the extra federal taxes they pay on health coverage.

The program was announced as part of the company's open enrollment for health, medical and dental insurance this month, and will go into effect next year, said company spokeswoman Ferris Morrison.

For heterosexual married couples, employer-paid health benefits for spouses are nontaxable, and employees can use pre-tax dollars to pay premiums. But for gay couples, the benefits are taxable and premiums must be paid with after-tax money.

The Bank of America program will make up that tax difference.

Large companies have long offered coverage to domestic partners. Bank of America has offered the coverage since 1998.

The Human Rights Campaign, a group that advocates for issues important to the lesbian, gay, bisexual and transgender community, reports that the majority of employers with more than 5,000 workers now offer health insurance to employees' same-sex partners.

Tax-reimbursement programs are much more recent, and are only offered by a handful of employers, including Bain & Co., Barclays Capital and Facebook, according to the Human Rights Campaign.

"It's fairly new and we see it growing. With each major corporation that adopts this practice, we hope that the rest of the corporate world will see this and follow suit," said Human Rights Campaign spokesman Paul Guequierre. "It's about basic fairness."

Morrison said the bank does not have an estimate of how much the average employee who insures a same-sex partner pays in extra taxes, or an estimate of how much the new program will cost the bank.

The Williams Institute, part of the UCLA law school, has pegged the average cost at $1,100 a year, Guequierre said, though the figure is not specific to any employer.