After 15 years together, Susan Tracy and Doris Brodhead were married in Boston Friday. The main reason they decided to tie the knot was for "the intangible benefits of having our kids know that we are an accepted, legal family," says Ms. Tracy, 43 years old, who runs a small public-affairs consulting firm in Boston. The couple has two young children.

But a bonus of the new legal tie is that they won't need to purchase two separate medical-insurance policies, a benefit that could save the family about $300 a month, Ms. Tracy estimates.

But the insurance and other benefits options for other gay and lesbian couples who decide to marry in Massachusetts, where same-sex marriages became legal May 17, may be less clear. Since the federal government doesn't recognize the legality of same-sex unions and gay and lesbian couples don't qualify for federal benefits, numerous employers will need to reconsider their benefits policies and what they are willing to offer such workers.

"It's creating an immense amount of complexity at this point because of the conflict between federal law and state law," says Nancy Mobley, president and chief executive officer of Insight Performance Improvement Inc., a human-resource-consulting firm in Dedham, Mass. "There's a lack of clarity as to how employers are supposed to be handling this."

The benefits for which same-sex married couples don't qualify are governed by federal laws that include the Employee Retirement Income Security Act, the Family and Medical Leave Act, and the Consolidated Omnibus Budget Reconciliation Act, known as Cobra. Employers can offer same-sex couples benefits that are equivalent to federally mandated ones, but they aren't required to do so by law.

For employers in Massachusetts, the new marriage ruling affects 401(k)s, retirement plans and personnel records, in addition to health-insurance benefits plans. There are also tax implications, since married gay employees can qualify as a spouse for the purposes of state taxes but not federal taxes.

Yet the complications don't end there. What benefits should a company based in Connecticut, where same-sex marriages aren't recognized, offer its employees who live and work in Massachusetts? What should the benefits be if an employee lives in Massachusetts but works in a neighboring state? What happens when an employee is transferred from Massachusetts to another state?

"The biggest struggle is going to be for organizations who are either housed in Massachusetts and have subsidiaries in other states, or employers headquartered outside of Massachusetts that have shops in the state," says David Namura, manager of state affairs for the Society for Human Resource Management in Alexandria, Va. He believes many multistate employers will be forced to adopt dual-benefits packages.

These benefits issues are bound to spur lawsuits, says Dave Wilson, an employment lawyer with law firm Robinson & Cole LLP in Boston. One self-insured labor union in Boston that represents 6,000 members has already effectively denied certain benefits to same-sex married couples, by clarifying the phrase "dependent spouse" to mean "a person of the opposite sex." "I would be shocked if someone doesn't bring suit against them," says Mr. Wilson.

Ironically, the marriage ruling could mean a decline in the number of employers in Massachusetts that offer domestic-partnership benefits, as they switch to offer one set of benefits to married couples, including same-sex couples.

Sandy Warren, director of human resources for Codman Square Health Center, in Dorchester, Mass., expects domestic-partnership benefits at the health center to be phased out sometime early next year, for example. "The reason why same-sex partners were able to get the insurance was that they couldn't get married," she says. Waiting until next year to change the policy "will certainly give folks the opportunity to marry," she adds.

Meanwhile, big employers in Massachusetts, such as Massachusetts General Hospital and MassMutual Financial Group, say they will continue to offer domestic-partnership benefits, even as they offer new benefits to same-sex married couples. "It really doesn't change the coverage, but it would change some of the tax implications," says Richard Goldstein, president and CEO of MassMutual Benefits Management Inc., a Springfield, Mass., subsidiary that administers MassMutual Financial's benefits. As for multistate issues, "it's something that we'd have to look at as it evolves," he says.

Some say the marriage ruling could also be a boon for small businesses that have wanted to woo gay and lesbian workers but found domestic-partnership coverage too costly.

The availability of benefits for same-sex couples gives small businesses "an opportunity to compete with larger employers who have historically been able to use domestic-partnership benefits as a competitive way to attract employees," says Devan Dewey, a director at the Greater Boston Business Council.