As Chicago became the latest city to tell Chick-fil-A it isn't welcome because its president doesn't support gay marriage, legal experts said the communities don't have a drumstick to stand on.

Chicago Mayor Rahm Emanuel became the second big-city mayor to blast the company over president Dan Cathy's comment last week that he is “guilty as charged” for supporting the traditional definition of marriage. Emanuel spoke up after Alderman Proco Joe Moreno announced he intends to block the chain from opening its second Chicago location over his stance.

But barring the popular fast-food restaurant over the personal views of Cathy is an “open and shut” discrimination case, legal scholars told FoxNews.com.

“The government can regulate discrimination in employment or against customers, but what the government cannot do is to punish someone for their words,” said Adam Schwartz, senior attorney for the American Civil Liberties Union of Illinois. “When an alderman refuses to allow a business to open because its owner has expressed a viewpoint the government disagrees with, the government is practicing viewpoint discrimination.”

"What the government cannot do is to punish someone for their words.”

- Adam Schwartz, American Civil Liberties Union of Illinois

The ACLU “strongly supports” same-sex marriage, Schwartz said, but noted that if a government can exclude a business for being against same-sex marriage, it can also exclude a business for being in support of same-sex marriage.

“But we also support the First Amendment,” he said. “We don’ think the government should exclude Chick-fil-A because of the anti-LGBT message. We believe this is clear cut.”

Jonathan Turley, a professor at the George Washington University Law School, said Moreno’s intentions raises “serious” constitutional concerns.

“It’s also a very slippery slope,” Turley told FoxNews.com. “If a City Council started to punish companies because of the viewpoints of their chief operating officers, that would become a very long list of banned companies.”

If Moreno did indeed put such a plan into action, it would be “excessive and likely unconstitutional,” Turley said.

Wilson Huhn, a professor and associate director of the Constitutional Law Center at The University of Akron School of Law, echoed Turley’s stance, saying that a denial on behalf of Moreno regarding a second Chick-fil-A restaurant in Chicago’s Logan Square neighborhood would “absolutely” violate the First Amendment.

“It would be an open and shut case,” Huhn said. “You can’t do that. They cannot be denied a zoning permit based upon the viewpoint of their CEO.”

Moreno and Emanuel can express their personal opinion on the matter, Huhn said, including the organization of boycotts and protests against the fast food chain.

“But if official action were taken against Chick-fil-A based upon their opposition to same-sex marriage by denying them permits or to prevent their restaurant from expanding, that would absolutely be viewpoint discrimination,” Huhn said.

Meanwhile, in a statement released Thursday, the owner and operator of Chicago’s only Chick-fil-A restaurant — which created 97 jobs in the past year — invited Emanuel to meet with her. The invitation came after Emanuel said opening a second location in the city would be a “bad investment” following Moreno’s statement.

In a statement to FoxNews.com, Sarah Hamilton, a spokeswoman for Emanuel, said that the mayor said that Cathy did not share Chicago’s values.

“He did not say that he would block or play any role in the company opening a new restaurant here,” Hamilton said in a statement to FoxNews.com. “If they meet all the usual requirements, then they can open their restaurant, but their values aren't reflective of our city.”

The Atlanta-based chain declined to comment for this story. Messages seeking comment from Moreno were not immediately returned.

Last week, Boston Mayor Thomas Menino told the Boston Herald that “it will be very difficult” for Chick-fil-A to obtain licenses for a restaurant in Boston. But on Thursday, Menino backed away from that threat, saying he won’t actively block the chain.

“I can’t do that,” he told the Herald. “That would be interference to his rights to go there.”

Despite the emotional issue of same-sex marriage, Cathy's position is not out of the mainstream. A USA Today/Gallup Poll in May showed 50 percent of Americans approved of gay marriage and 48 percent opposed it. That poll was taken one day before President Obama, who had previously said he was against same-sex marriage, but that his position was "evolving," came out in favor of it.

Evangelist Billy Graham on Thursday issued a statement in support of Cathy and Chick-fil-A for its “strong Christian” faith.

“I've known their family for many years and have watched them grow Chick-fil-A into one of the best businesses in America while never compromising their values,” the statement read. “Each generation faces different issues and challenges, but our standard must always be measured by God's word. I appreciate the Cathy family's public support for God's definition of marriage …  As the son of a dairy farmer who milked many a cow, I plan to 'Eat Mor Chikin' and show my support by visiting Chick-fil-A next Wednesday."