Some law firms are rolling out new perks aimed at reimbursing their gay employees for the tax liability they incur when they elect to add domestic partners to their health benefits plans.

The latest firm is McDermott Will & Emery, which yesterday said that beginning in 2011 it would provide a tax “gross-up” payment for its employees in same-sex domestic partnerships. McDermott followed Morrison & Foerster, which last month said it would provide a similar payment to assist its staff and non-partner attorneys who elect domestic partner health benefits.