Sen. Rob Portman has his first opportunity to support gay rights legislation on Thursday, when a bipartisan group of senators plans to reintroduce the Employment Non-Discrimination Act.

In March, the Ohio Republican became the first GOP senator to support gay marriage, but Portman said Wednesday that he is still unsure whether he will support the legislative effort to expand federal equal opportunity labor laws to protect gay and lesbian workers.

Portman has talked briefly with Sen. Jeff Merkley, D-Ore., one of the five co-sponsors of the bill, but that conversation was not particularly substantive on either side.

“We haven’t had any extensive discussions yet,” Portman said Wednesday. “I need to look at it.”

Merkley, along with Democrats Tammy Baldwin of Wisconsin and Tom Harkin of Iowa and Republicans Mark S. Kirk of Illinois and Susan Collins of Maine are the original co-sponsors of the bill being introduced.

“Senator Portman is strongly opposed to discrimination and is looking at proposals to address it,” Portman spokeswoman Caitlin Dunn said in a statement. “He is concerned about excessive reliance on litigation as a tool for social change, but he has not studied the most recent version of ENDA.”

In practice, a markup of the most recent version of EDNA likely will not happen until May or June. And Portman does not serve on the Health, Education, Labor and Pensions Committee that has jurisdiction over the bill.

Though he is one of two Republican senators to support marriage equality — Kirk is the other — it is possible Portman could oppose the legislation on states’ rights grounds.

According to a recent study by the Center for American Progress, 21 states have labor laws on the books to protect gay and lesbian workers and give them legal recourse to deal with employment discrimination. The study does not consider Ohio one of those states, though it is in a group of 10 states cited as having some protections that are “weak.” The Ohio law only protects state employees.

“We consider these policies weak because they only apply to public employees and/or omit gender identity coverage. It is important to recognize the way in which these policies are weaker than [other] laws — namely they can be rescinded by the governor (which means the protections are not necessarily permanent), and as we will see in the next section, offer no legal recourse,” the CAP study found. “In the past four years, for example, Louisiana Gov. Bobby Jindal (R) and Virginia Gov. Bob McDonnell (R) have rescinded executive policies.”

Niels Lesniewski contributed to this report.