The chairmen of the White House's debt-reduction commission are making changes to their draft proposal in a move to broaden support before Wednesday's vote, The Wall Street Journal reported.

Democrat Erskine Bowles and former Republican Sen. Alan Simpson need 14 of the 18 members of the National Commission on Fiscal Responsibility and Reform to support their proposal in order to issue a formal recommendation, the newspaper said.

The recommendation could then be voted on by Congress.

Winning 14 votes appears unlikely, the newspaper said, citing people familiar with the matter.

The details of the changes were not disclosed, but they were designed to incorporate suggestions made by some of the members of the commission, the newspaper said in its electronic edition.

Earlier this month, Bowles and Simpson proposed a series of changes to U.S. spending and tax policy in areas such as Medicare, Social Security, defense spending that would hold down the growth of the federal debt by roughly $3.8 trillion by 2020.