DOMA defines "marriage" as a heterosexual union and defines "spouse" as "a person of the opposite sex who is a husband or a wife." These definitions apply for purposes of all federal laws, including the Employee Retirement Income Security Act ("ERISA") and the Internal Revenue Code.  Accordingly, same-sex couples (whether married or protected by another's state's domestic partnership laws) are not protected by federal laws such as COBRA (continued health coverage for individuals who lost their job), HIPAA (health information privacy), ERISA (retirement security), FMLA (family and medical leave), and the like (but could be protected by some states' counterparts to those laws, where they exist). Similarly, same-sex married couples do not experience the favorable federal tax treatment enjoyed by their heterosexual counterparts. However, DOMA doesn't prohibit an employer from voluntarily extending coverage and benefits to same-sex spouses, even though such benefits may not come with the same federal tax incentives and other cost savings available to heterosexual married couples.
Health Benefits
Employee benefits plans covered by ERISA preempt Oklahoma law such that, for example, currently a same-sex spouse participating in family coverage under an ERISA-governed self-insured group plan is not entitled to a federal pretax deduction for the cost of the premium. This will change if the DOMA section defining marriage is overturned.  However, ERISA has a "savings clause" that provides that it does not preempt state laws relating to insurance. Thus, employee benefit plans that offer coverage through an insurance contract (including contracts for health, dental, vision, and life insurance, as examples) subject to the insurance laws of a state, like Oklahoma, that does not recognize same-sex marriage may not have obligations to same-sex couples. That being said, businesses that are self-insured are governed by ERISA and do not have obligations under state law, even if the plan is administered by an insurance company such as Blue Cross Blue Shield.

Family Medical Leave
The general consensus has been that the Family Medical Leave Act (FMLA) does not require equal treatment between same-sex and heterosexual married couples.  However, if DOMA is overturned, this issue will likely be brought to the Courts. Some employers could voluntarily offer medical leave to an employee to care for his or her same-sex spouse, or wait for further guidance from the federal courts or Congress.

Tax Consequences Highlights
The Internal Revenue Code adopts the definition of "spouse" from DOMA and excludes same-sex spouses. Consequently, if overturned, an employee or his/her spouse may NOT be taxed on typically excludable "spousal" benefits unless another basis for exclusion exists.