The appointed panel that ran the program, the Board of Commerce and Industry, handed out nearly $10 billion in local tax exemptions between 2008 and 2016, but its actions were rarely covered in the press. Many Louisianans had no idea what the board did.

“Nobody knew about it,” Ms. Collins said. “It had gone on for so long that people had forgotten.”

Together Baton Rouge and its sister organization, Together Louisiana, argue that the industrial tax breaks starve local schools and governments of badly needed funds and leave them unable to lift a state mired toward the bottom of national rankings on education, crime and infrastructure. In Baton Rouge, one in four residents lives in poverty.

Their message has found an audience: Together Louisiana’s YouTube video about the exemptions, posted in November and titled “Why Louisiana Stays Poor,” has been viewed more than 600,000 times.

A few days before the Baton Rouge school board vote, the groups held a meeting at St. Mary Baptist Church to organize opposition to the Exxon Mobil application. Scores of people crammed into a Bible study classroom decorated with maps and photos of the Holy Land.

Edgar Cage, who organized the meeting, was careful to say that no one was accusing Exxon Mobil of any wrongdoing. “All we’re saying is, we want a change,” he said. “We want a balance.”

Business leaders reacted strongly to the Baton Rouge vote because they are worried about much more than just how a few capital improvements are taxed. As much as $90 billion in oil and gas industry investments could come the state’s way in the next decade, driven in large part by the boom in domestic shale gas drilling, according to David Dismukes, executive director of the Center for Energy Studies at Louisiana State University.

By itself, Dr. Dismukes said, the school board’s vote “was not a big deal — but the precedent it sets is going to be really big for these projects on the drawing board that are $100 million or $200 million.”