Cash-strapped could lose another £20 million as a result of a new "fair" funding system proposed by the Government, it has been claimed.
The revelation the service faces further cuts comes after the force announced plans to "significantly reduce" the number of police community support officers (PCSOs).
Earlier this month, Police Minister Mike Penning launched a consultation about a new system to determine how national police funding would be divided between different forces.
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There is widespread agreement the existing system is too complex and Mr Penning said its replacement would be "fair, robust and transparent".
But the Post understands an initial analysis of the Government's proposals by accountancy firm PwC, commissioned by West Midlands Police, has found it could actually lead to funding for West Midlands Police being cut by £20 million or more. The study is ongoing.
Jack Dromey, Labour's Shadow Police Minister and MP for Erdington, has written to Mr Penning asking him to publish the Government's own calculations which would confirm how each force is likely to be affected.
The National Audit Office (NAO), an independent body set up by Parliament to scrutinise public spending, has warned West Midlands Police is already hit harder than other forces by spending cuts so far.
Its total spending power was cut by 23 per cent, almost a quarter, over the past five years while others had suffered less drastic reductions, with funding for Surrey Police down by just 12 per cent in the same period, the NAO said.
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And along with other police forces, West Midlands Police is gearing up for an announcement on November 25 when Chancellor George Osborne reveals how police services will be affected by his plan to reduce spending on public services by £20 billion over the next five years.
Mr Dromey said: "We are reaching a crunch point."
Along with other Labour MPs in the region, he is urging the Government to ensure the West Midlands gets a better deal in November's announcement.
He said: "Everything this government does is characterised by unfairness.
"The West Midlands has been hit twice as hard as Surrey and now, to add insult to injury, the Government's 'fair funding' review will see our region lose another £20 million.
"The public will see far fewer bobbies on the beat and the numbers of PCSOs will be slashed, rightly causing alarm in communities all over the West Midlands."
But West Midlands Police chief constable Chris Sims came in for criticism after he announced cuts to PCSOs.
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The chief constable did not give the number of PCSOs that would be lost but in a statement said the amount would be considerably lower by 2020.
"We haven't finalised our eventual numbers of PCSOs but it is clear there will need to be a significant reduction in the numbers between now and 2020," he said.
Black Country MP John Spellar (Lab Warley) said: "Over recent years, crime has fallen and public confidence has risen. Now, drastic cuts from the Tory Government are putting all this at risk.
"However, police chiefs are making the wrong call by cutting back on visible policing."