NKU regents Monday approved the benefits package, which would allow employees to add family members or others to their plan when a spouse is not covered.
It would require that the covered person live in the employee's household for at least 12 months and be "financially interdependent" with the employee. The employee would pay the cost.
State Sen. Damon Thayer, R-Georgetown, chairman of the Northern Kentucky Legislative Caucus, supported a bill earlier this year to ban universities from offering benefits to same-sex partners of employees.
While that bill never came to a House vote, Thayer said the ban would have broad support both in the legislature and with the public.
"I find NKU's decision disappointing and a bit of slap in the face of the will of the people of Kentucky," Thayer said.
State Rep. Dennis Keene, D-Wilder, said the decision is NKU's and state government should not be involved.
"I know Northern will take a lot of heat for doing this, particularly from those in the Republican Party," Keene said. "But legislators should stay out of it. Northern has a lot of courage to be doing this. It is their decision to make."
NKU has mostly avoided the political battles so far, preferring to let the University of Kentucky and the University of Louisville take the lead.
But NKU officials said the extended benefits would help attract and retain better employees. They noted that it could cover an adult child or a sibling as well as a live-in partner of either sex.
The University of Cincinnati extended full benefits to domestic partners of about 6,500 employees last fall.
"We're not supporting any particular lifestyle or judging anything," Lori Southwood, NKU's senior director of human resources, told regents. "We're acknowledging that one offer does not fit all."
The vote to approve was 7-2, with regents Frank Downing and Joyce Griffin voting against it.
During debate on the issue, Bob Zapp, who is rotating off the university's board, called it a "competitiveness issue."
Downing said NKU should stick with its current position, which he called "the moral choice."
Regent Nancy Kremer, the St. Luke Hospitals executive who led a group that studied the issue, said the new policies endorse only the benefit to NKU employees.
"We've made it so broad and so balanced, and the whole intent here is health and wellness," she said.
Under the proposal, the employee will pay the full cost of the extended coverage. An employee could not cover both a spouse and someone else.
In other action, NKU regents approved the administration's plan to increase tuition 9.68 percent for in-state undergraduates next year. NKU presents the request to state officials later this week.
They also approved the plan, announced last week, to be annexed by Highland Heights. In return, Highland Heights will sell its city building to NKU for $1 and build NKU a $6.5 million soccer stadium.