Bill Miller, national political director for the chamber, charged in a statement that Boxer has made "California businesses less competitive, costing the state jobs." Politico reported the ad will run statewide for two weeks.
The San Francisco Chronicle opted this weekend for a non-endorsement, saying voters were left with a "deeply unsatisfying choice" on the fall ballot.
The TPM Poll Average of this race has Boxer ahead 47.5%-Fiorina 44.3%. The two candidates face off again in a debate Wednesday.
Watch the chamber ad: