"Both Elizabeth and Sen. Brown have released multiple years of tax returns that she believes give voters an understanding of each candidate's financial circumstances," Warren aide Alethea Harney said in a statement.

Brown campaign manager Jim Barnett said Warren "deserves a pair of gold medals for backpedaling and hypocrisy" and renewed the campaign's call for Warren to match Brown and release six years of tax returns.

"In her fumbled attempt to smear Scott Brown, she has only raised new questions about why she continues to hold back tax records requested by the media," Barnett said in a statement. "Scott Brown complied with this request; Elizabeth Warren did not."

In April, both candidates released some of their returns.

Brown made six years of returns available for inspection by journalists at his campaign headquarters at the time, but didn't post them online or allow copies to be removed.