Federal Reserve Chairwoman Janet Yellen on Tuesday wrote a letter to House Speaker Paul Ryan and House Democratic leader Nancy Pelosi, saying that Congress should reject a reform bill on the Fed's transparency.

"The bill would severely impair the Federal Reserve's ability to carry out its congressional mandate and would be a grave mistake, detrimental to the economy and the American people," she wrote.

Yellen pointed out that the bill would lead to "poor economic outcomes".