BOSTON (AP) -- U.S. Sen. Elizabeth Warren has filed a bill she said would let millions with existing federal student loans to refinance at the lower interest rates currently offered to new borrowers.

Warren said Tuesday that many of those with outstanding loans have interest rates of nearly 7 percent or higher for undergraduate loans while students taking out new undergraduate loans pay a rate of 3.86 percent.

The Massachusetts Democrat said the nation’s $1.2 trillion in student loan debt is "crushing young people and dragging down our economy." She would pay for her proposal with a tax increase on wealthy Americans

The bill is co-sponsored by more than 20 fellow Democratic senators.

Massachusetts U.S. Rep. John Tierney joined with fellow Democrat, California Congressman George Miller, to file a similar bill in the House.