In-N-Out is a private company and does not disclose its sales.

There is little evidence that political beliefs and contributions hurt businesses in a meaningful way, said Nick Setyan, an analyst at Wedbush, a financial firm focused on the restaurant sector.

“These tend to be passing fantasies,” Mr. Setyan said. “For every liberal that may not go to Carl’s Jr. or an In-N-Out or Chick-fil-A there’s probably a conservative that will go an extra time to support that company.”

Has In-N-Out always supported the G.O.P.?

The company said it had made equal contributions to both Democratic and Republican political action committees in California.

“While it is unfortunate that our contributions to support both political parties in California has caused concern with some groups, we believe that bipartisan support is a fair and consistent approach that best serves the interests of our company and all of our Customers,” Arnie Wensinger, the executive vice president, said in a statement.

The conservative leanings of the company are no secret, said Stacy Perman, the author of “In-N-Out Burger: A Behind-the-Counter Look at the Fast Food Chain That Breaks All the Rules.” Rich Snyder, one of the founders’ sons who ran the company until his death in 1993, was a well-known G.O.P. supporter, and this episode is unlikely to make a dent in business, Ms. Perman said.

“They have a surprisingly diverse fan base politically across the spectrum,” she said. “They have their truck at the Vanity Fair Oscar Party.” Ms. Perman also noted that the company has “weathered economic shifts and personal tragedy, and they’re still pretty strong.”

Founded in 1948 by Harry and Esther Snyder in Baldwin Park, Calif., In-N-Out was known for making freshly prepared burgers long before the recent wave of fast-casual food pushed other corporations into making their menus healthier and fresher. It is also known for the Bible verses on its packaging. It is now run by Lynsi Snyder, the founders’ granddaughter, who was sued by the company’s vice president in 2006 for trying to seize control of the company.