The review, out of the Leeds agency Poulter Partners, was planned before the northern retailer launched its audacious £2.9 billion bid for Safeway last month, and is part of a drive by Morrisons to increase its profile in the south of England.
News of the bid by the country's fifth-largest supermarket helped to lift Morrisons' January sales figures by 5.2 per cent and boosted shares by 10p to 169p.
Michael Bates, the marketing services controller at Morrisons, confirmed the supermarket chain was reconsidering its agency relationship, but declined to elaborate.
"Our advertising arrangements are under review and we have approached some agencies but I can't comment further," he said.
He refused to confirm whether the incumbent, Poulter, would be included in the final line-up and would not comment on the likely timing of a new appointment.
However, he added that Morrisons' relationship with its media agency, Mediaedge:cia, was not affected by the advertising review.
Morrisons is 30 per cent family owned. Most of its 119 stores are based in the north of England but it is keen to bolster its profile in the south.
The Bradford-based chain triggered a bidding war for Safeway, the country's fourth-largest supermarket chain, in January with its all-share bid. Since then, Sainsbury's, the Walmart-owned Asda and Tesco have all thrown their hats into the ring.
Last May, Morrisons ran a national TV campaign promoting its fresh food offer.