RBS had said last year that it would sell 20-25 percent of Citizens by the end of 2014 through an U.S. IPO as the bank faces pressure from British regulators to bolster its capital and sell off non-core assets.

Citizens, which provides retail and commercial banking services to about 5 million customers, said in the filing that the U.S. Fed in March objected to its capital plan submitted as part of the stress test, or the Comprehensive Capital Analysis and Review.

Citizens also said two of its banking units are subject to consent orders from regulators in connection with findings of deceptive marketing and implementation of its checking account and funds transfer services.

Morgan Stanley, Goldman, Sachs & Co and JPMorgan are the lead underwriters for the IPO, the company said in the filing with the U.S. Securities and Exchange Commission on Monday.

The filing did not reveal how many shares the company planned to sell or their expected price.

Citizens has $122.2 billion of total assets and about 1,370 branches in 12-states across the New England, Mid-Atlantic and Midwest regions.

The amount of money a company says it plans to raise in its first IPO filings is used to calculate registration fees. The final size of the IPO could be different.