Engstrom told the audience at a Committee of 100 meeting that the group would support Landrieu in her fight to win re-election, according to The New York Times' Joe Nocera.
Chamber of Commerce spokeswoman Blair Latoff Holmes told TPM in an email on Monday "no decisions have been made in the LA Senate race."
Landrieu's major Republican challenger is Rep. Bill Cassidy (R-LA).
A U.S. Chamber of Commerce scorecard said Landrieu votes for pro-business legislation more often than Sen. Ted Cruz (R-TX), according to The Wall Street Journal.
In previous elections, the Chamber has spent money on television ads supporting Landrieu's campaign. In April, the Chamber's senior political strategist, Scott Reed, said it was too early to make a decision on whether they would support Landrieu or not.
This post has been updated.