The commercial from Capital One had most of the identical guarantees that different banks supply for high-yield financial savings accounts: There have been no charges, no minimal deposits and the cash would earn rather more in curiosity than in conventional financial institution accounts.

“What’s the catch? There’s none,” the financial institution boasted.

However, based on a lawsuit filed in opposition to Capital One on Tuesday by the Client Monetary Safety Bureau, there was one, and it value depositors greater than $2 billion.

For years, Capital One held pursuits artificially low within the high-yield product, to 0.30 p.c yearly final summer season, as an illustration, even because the Federal Reserve raised charges above 5 p.c.

Banks are typically permitted to pay as little in curiosity as their clients will allow, however Capital One went too far, based on the lawsuit, by intentionally complicated its clients about its merchandise. The financial institution operated two separate, almost identically named account choices — 360 Financial savings and 360 Efficiency Financial savings — and forbade its staff to volunteer details about or advertising 360 Efficiency Financial savings, the higher-paying one, to present clients.

In its lawsuit, the buyer bureau referred to as the apply misleading, abusive and unlawful. “The one factor that has ever meaningfully distinguished 360 Efficiency Financial savings from 360 Financial savings is the previous product’s greater rate of interest,” the lawsuit mentioned.

A Capital One spokesman, Sie Soheili, declined to touch upon the precise allegations within the go well with, however he mentioned the financial institution, the nation’s ninth largest, disagreed with the claims and would dispute them in courtroom. The financial institution is making an attempt to finish a deal to amass the credit-card issuer Uncover.

The lawsuit is the most recent in a flurry of last-minute admonishments from the buyer bureau earlier than the inauguration of President-elect Donald J. Trump. Republicans largely detest the company, which was based in 2011 and which they’ve mentioned is an instance of bureaucratic overreach, although Mr. Trump stored it alive throughout his first time period.

Almost each working day for the previous month, the company has filed a lawsuit or proposed a rule change or different pending motion in opposition to a serious monetary establishment. The lawsuit on Tuesday was not the company’s first in current weeks involving Capital One; final month, the regulator accused Zelle, the money-transfer app co-owned by the financial institution, of failing to guard its clients in opposition to greater than $800 million in fraud.

Mr. Soheili mentioned in an announcement that the regulators had been persevering with their “current sample of submitting Eleventh-hour lawsuits forward of a change in administration.”

A spokeswoman for the buyer bureau, Tia Elbaum, responded: “The place we see violations of the legislation, we’ll take motion.”