Gina Fusco, ING Direct sales and marketing director, said: "Since we launched in 2003, MPG has played a key role in establishing our simple, straightforward and no-catches savings product.
"Now that we have passed the important 1m customer milestone and new products are on the horizon, it is appropriate and best practice to review our current media handling arrangements."
ING Direct is operational in nine countries and has more than 15m customers. The company launched in UK in May 2003.
Marc Mendoza, managing partner at MPG, said: "We are proud of the work we have done in establishing the ING Direct brand. We are looking forward to continuing a successful relationship and fully understand that a financial services company that has now reached this size would want to undertake a benchmarking exercise."
MPG is on a shortlist of unnamed agencies in what the firm says will be a "considered and a speedy review process". The review will be handled through the AAR.
ING Direct is part of International Netherlands Group, one of the world's largest financial services organisations, operating in 60 countries with more than 115,000 employees.
The company has no high-street presence, therefore its costs are kept down and there are no restrictions on customers accessing their funds.
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