 -- Indiana Gov. Mike Pence stirred fierce backlash from critics by signing a "religious freedom" law on Thursday, and he might have also shaken up the 2016 presidential race in the process.

The former congressman and potential 2016 presidential candidate signed into law a controversial state Senate bill that simply states the government can't interfere with people and businesses exercising their religious beliefs. Religious freedom is already protected under the U.S. Constitution, and Pence posed the new law as an innocuous affirmation of the Supreme Court's Hobby Lobby ruling, against the mandate for employer-provided birth-control coverage under Obamacare.

Known as a social conservative, Pence has said he's considering a White House run and will reportedly decide sometime this spring.

The bill has sparked intense backlash online, but it's won a very important fan for Pence: Bob Vander Plaats, the noted Iowa-caucus kingmaker who heads up the FAMiLY Leader, a socially conservative group that exercises notable political influence in the critical primary-campaign state.

"I think it definitely boosts his credibility, not just with a group like ours, but for any freedom-loving American who wants to have a full-spectrum conservative in the White House," Vander Plaats told ABC News.

Since Pence signed the bill, critics have lashed out at the governor online. Miley Cyrus posted a photo of Pence on Instagram, calling the governor an "a**hole." Businesses reportedly lobbied against the bill, and Yelp's CEO said it sets a "terrible precedent."

Pence defended the law at a press conference on Friday after he signed it, saying it is "not about discrimination" and pointing to similar laws in other states, and to the federal Religious Freedom Restoration Act signed into law by president Bill Clinton. Pence said he thinks there has been a lot of "misunderstanding" surrounding the bill.

Critics see it differently. The bill "absolutely does" give a green light to discrimination, according to Jenny Pizer, national director of law and policy at Lambda Legal, an LGBT legal-defense and advocacy group.

"Many people take these bills as a message that the usual rules to not apply, and that other people should endure mistreatment if that is based on a religious motive," Pizer said.

At issue is whether businesses can discriminate against gay, lesbian, bisexual, transgendered, and transsexual clients: for instance, wedding photographers, wedding-cake bakers, or florists who may see a gay wedding as contradicting religious beliefs against gay marriage. In some places, businesses already can refuse to serve gays and lesbians, Pizer said, with nondiscrimination laws on the books in fewer than half the states and a dozen counties in Indiana. For Pizer and other critics, the concern is that the bill will green-light discriminatory attitudes.

For Pence, the decision could bring embarrassment for his state--the NCAA issued a strongly worded statement that it is "concerned" about the law's effects, as the men's basketball Final Four heads to Indianapolis next weekend--but it could also provide a political windfall among activists like Vander Plaats in key primary states.

"This isn't about driving through McDonald's and saying you can't order a Big Mac 'cause you're gay," Vander Plaats, who says he's examining Pence along with other candidates, told ABC. The social-conservative vote will likely be sought by the likes of Mike Huckabee, Ted Cruz, Rick Santorum, Bobby Jindal, Rick Perry, and a handful of others in the 2016 GOP race. Huckabee and Santorum each carried Iowa with Christian-conservative messages in 2008 and 2012, respectively.

"Gov. Pence, he did a great job signing that legislation, and I truly believe this will be a big issue in the 2016 race, the idea of religious freedom," Vander Plaats said.