The review comes after the brewer merged its SABMiller Brewing and Molson Coors operations in July of this year. The company is said to be saving $500 million in costs because of the merger.
Only agencies that are currently part of the Miller and Coors roster shops are open to the review, which includes Starcom, Initiative and Draftfcb.
The review, which is being led by MillerCoors' marketing services vice-president, Jackie Woodward, is expected to be concluded by late November.