Democratic presidential front-runner Hillary Clinton’s campaign offered new details about her paid family leave plan Thursday, and continued to reject the leading proposal in Congress because it relies on a small increase to the payroll tax.

The Clinton campaign said its plan would closely resemble the pending legislation, called the Family Act, in other ways. Like that legislation, it would include 12 weeks of paid family and medical leave and a minimum two-thirds wage replacement rate.

Her announcement came a day before her rival for the nomination, Sen. Bernie Sanders, plans a news conference in Iowa to discuss his paid family leave program. He has been highly critical of Mrs. Clinton for her rejection of the pending bill, which he supports.

On the stump, Mrs. Clinton has been hammering Mr. Sanders by saying she’s the only candidate who won’t raise middle class taxes. Supporting the existing family leave legislation, as Mr. Sanders does, would abrogate that claim.

Instead, a senior Clinton adviser said Thursday that she would pay for the new government benefit with increased taxes on the wealthy.