Attorney General Ken Paxton announced Thursday his office has sent a letter to the mayor and city council informing them of the investigation.
RELATED: Chick-fil-A banned from San Antonio airport with 6-4 council vote
Paxton said the city may have violated federal law by banning Chick-fil-A based on the company's religious beliefs. He is pushing for the U.S. Department of Transportation to investigate potential federal violations.
On March 21, San Antonio City Council voted 6-4 to exclude the fast food chain from a 7-year concession agreement.
District 1 City Councilman Robert Trevino said the motion to ban Chick-fil-A was made to send a message that San Antonio is not open to anti-LGBTQ behavior.
"The City of San Antonio's decision to exclude a respected vendor based on the religious beliefs associated with that company and its owners is the opposite of tolerance," Attorney General Paxton said. "The city's discriminatory decision is not only out of step with Texas values, but inconsistent with the Constitution and Texas law."
A report released last week by ThinkProgress shows Chick-fil-A donated $1.8 million to groups that discriminate against the gay community.
Chick-fil-A said in a statement that it was disappointed by the vote, and would have liked to have had the chance to speak with the city council before the decision.
Video in story is from previously published report.