David Axelrod, Obama's top strategist, called the New York senator a "veteran of non-disclosure," suggesting she hasn't been fully scrutinized, a charge she has leveled against Obama.
The Clinton campaign countered the Illinois Democrat's more aggressive campaign strategy amounts to attacking Clinton's character and ethics.
"This is a tried and true technique of the Obama campaign, which has repeatedly shifted negative when they find the momentum working against them," Mark Penn, Clinton's top strategist, told the Chicago Tribune.
Obama's campaign repeated its call for Clinton to release her tax records, earmark requests, documents from the William J. Clinton Presidential Library and names of donors to the library and a foundation.
"What is Senator Clinton hiding and what is lurking in those documents?" Robert Gibbs, Obama communications director, asked.
Clinton has said she will release the tax documents in mid-April.