The Fed on Thursday said it would pump $40 billion into the U.S. economy each month until it saw a sustained upturn in the weak jobs market. (Read more: Fed's 'QE Infinity' — Four Things That Could Go Wrong)

In its downgrade, the firm said that issuing more currency and depressing interest rates through purchasing mortgage-backed securities does little to raise the U.S.'s real gross domestic product, but reduces the value of the dollar.

In turn, this increases the cost of commodities, which will pressure the profitability of businesses and increase the costs of consumers thereby reducing consumer purchasing power, the firm said.

In April, Egan-Jones cuts the U.S. credit rating to "AA" from "AA+" with a negative watch, citing a lack of progress in cutting the mounting federal debt.

Moody's Investors Service currently rates the United States Aaa, Fitch rates the country AAA, and Standard & Poor's rates the country AA-plus. All three of those ratings have a negative outlook.