Officials said they notified employees before putting up the flag, which was raised at the Fort Wayne plant earlier in the week, WANE-TV, Fort Wayne, reported Thursday.
"Currently the GM PLUS rainbow flag is flying for one week in support of Pride month. It's our hope that ongoing support of our employees will foster constructive dialogue on the importance of diversity at GM," the company said in a statement.
Chris Gunderson, president of the Indiana University - Purdue University Fort Wayne United Sexualities group, applauded the company for flying the flag.
"It makes a statement that they're inclusive and that they celebrate diversity within their company," Gunderson said.