Citizens Financial Group Inc. revealed yesterday that it is engaged in an intensive shift to mobile-centric retail banking that has caused significant growth in adoption of its alternative banking channels, according to the bank’s filing for an initial public offering.

Citizens, a unit of Royal Bank of Scotland, filed for the IPO yesterday.

Citizens reports that it is consciously reducing its branch footprint “while building out self-service channels through online and mobile banking and person-to-person payments.” The result is the bank’s mobile banking channel has experienced a 33% increase in active mobile customers over the past year.

At the end of 2013, Citizens had 1.8 million online banking customers and 521,000 active mobile customers, according to the filing. By comparison, Bank of America has about 15 million active mobile users.

Citizens indicated that its mobile banking strategy is largely platform agnostic, between Android and Apple smartphones and iPads.

But the bank indicated in the S-1 that there are risks in its technology-first strategy. Here’s how the bank described it:

In Consumer Banking, the industry has become increasingly dependent on and oriented towards technology-driven delivery systems, permitting transactions to be conducted by telephone and computer, as well as through online and mobile channels. In addition, technology has lowered the barriers to entry and made it possible for non-bank institutions to attract funds and provide lending and other financial services in our footprint despite not having a physical presence within our footprint. Given their lower cost structure, these institutions are often able to offer rates on deposit products that are higher than what may be average for the market for retail banking institutions with a traditional branch footprint, such as us.

The IPO of Citizens, which serves about 5 million total customers, is expected to raise about $100 million.