Three Birmingham MPs are set to compete over two constituencies when the city loses a seat in the House of Commons.
The existing 11 constituencies are to be reduced to ten because of a falling population.
As a result, the Labour Party faces a long internal battle to see which sitting MPs survive, and who is axed.
Lynne Jones, MP for Selly Oak, Steve McCabe, MP for Hall Green, and Roger Godsiff, MP for Sparkbrook and Small Heath, are affected.
Their three constituencies have been reduced to two, in proposals drawn up by the Boundary Commission.
The MPs will be forced to compete for nominations to stand as Labour candidates in the next General Election, unless one of them voluntarily steps down.
The party's National Executive Committee, which includes Tony Blair, Gordon Brown and John Prescott, as well as West Midland MEP Michael Cashman, is to instruct local officials on how to make the selection.
Originally, the Commission recommended abolishing Sparkbrook & Small Heath, and distributing the areas it covered among neighbouring constituencies.
But this month it published radical new proposals which included drastic alterations to all three seats.
The Hall Green seat will consist of four council wards - only one of which, also called Hall Green, is currently part of the seat.
It will gain the Sparkbrook and Springfield wards from Roger Godsiff's Sparkbrook & Small Heath constituency, potentially giving Mr Godsiff a strong claim to the seat.
At the same time, the wards of Billesley and Brandwood move from Hall Green to Selly Oak.
This means the majority of Steve McCabe's current electorate in Hall Green will become part of the Selly Oak constituency, giving the MP a potentially strong claim to that seat.
Lynne Jones has a strong claim to Selly Oak, but could also claim the nomination for Hall Green - because one of her wards, Moseley & Kings Heath, is to become part of that constituency.
Under Labour Party rules, a sitting MP whose constituency is changed can apply to be the candidate in any seat which includes part of their old constituency.
A fourth seat, Yardley, currently held by the Liberal Democrats, has also been significantly altered.
However this is expected to make it a safer seat for the Lib Dems, and no sitting Labour MPs are likely to want to stand there.
Smaller changes have also been made to a number of other seats in the city.
Dr Jones said: "My constituency is meeting to discuss whether we want to challenge the new boundaries."
A spokesman for the Boundary Commission said: "It is still possible to lodge objections to the changes." A Labour Party spokeswoman said: "It would be possible for more than one sitting MP to apply to be a candidate in any of the seats affected.
"We are waiting for guidance from the National Executive Committee on how exactly the candidate would be decided, if this happened."
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