Just one Black Country MP — Labour's Tom Watson — is still supporting the Alternative Vote in the referendum that will be held on Thursday.
The member for West Bromwich East is the one regional MP who wants people to rank candidates in order of preference and sweep away the current "first past the post" system.
All Conservative MPs in the region are against it and nationally the Labour party is split with leader Ed Miliband in favour, but many MPs not.
Under AV a winner is only declared once he or she has at least 50 per cent of the votes. The majority is gained by eliminating the candidate with the least votes and re-allocating those ballots to the voters' second choices.
Mr Watson said: "Other MPs are genuinely convinced that the status quo is fairer and I respect their positions.
"I'm supporting AV because I see it as a key progressive step that makes MPs a little more accountable to their constituents."
In the Black Country all other Labour MPs have signed a letter urging people not to back AV in the referendum, which was demanded by Liberal Democrat leader Nick Clegg in return for supporting David Cameron in the coalition Government.
Wolverhampton Liberal Democrat councillor Robin Lawrence, who finished third in the election for the MP for Wolverhampton South West last year, said: "The proposed new system will make MPs work harder and it will be much easier to vote out an MP who performs poorly.
"If people want their MPs to work hard and be more accountable to them, they need to turn out in large numbers on May 5."
Chris Kelly, Conservative MP for Dudley South, and Ian Austin, Labour MP for Dudley North, are both calling for their constituents to vote no.
Labour MPs Adrian Bailey of West Bromwich West, Pat McFadden of Wolverhampton South East, Emma Reynolds of Wolverhampton North East, John Spellar of Warley, David Winnick of Walsall and Valerie Vaz of Walsall South are all voting no.
Conservatives Paul Uppal of Wolverhampton South West, Richard Shepherd of Aldridge and Brownhills, Aidan Burley of Cannock Chase, Jeremy Lefroy of Stafford, Michael Fabricant of Lichfield, Margot James of Stourbridge and James Morris from Halesowen and Rowley Regis, are all against AV as well.