Six Democrats whose support is crucial to a U.S. Senate plan to replace government-owned mortgage firms Fannie Mae and Freddie Mac have decided they won’t support the proposal without major revisions, dimming its chances of becoming law this year.

The lawmakers agreed in a private meeting Thursday that they wouldn’t support the bipartisan proposal to replace the finance companies with a government re-insurer, according to three people familiar with the meeting. A lack of Democratic consensus scuttled plans last week to approve the bill by the Senate Banking committee, whose chairman yesterday vowed to continue seeking votes.