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More than 100 House Republicans have vowed not to vote for any spending bill that doesn't protect the Pentagon from mandatory seqestration cuts at the heart of the controversy that has stalled the budget process.

In a letter Monday to House Speaker John Boehner and Majority Leader Kevin McCarthy, the 102 Republicans led by Mike Turner of Ohio, a House Armed Services subcommittee chairman, said the $561 billion in Pentagon spending requested by President Obama is the minimum they will accept.

"In this increasingly unstable world, it is clear that further reductions to national defense accounts are irresponsible," they wrote.

President Obama's fiscal 2016 defense request included $561 billion in baseline funding, well above sequestration-related spending caps. The letter says the lawmakers will block the bill if the amount of base budget funding is anything under $561 billion. In order to skirt spending caps, the appropriations bill would pay for some baseline accounts by using a war funding account, which isn't subject to spending caps.

The letter puts GOP leaders in both chambers in a tight spot, between the demands of those who signed it and Democrats who object to what they call a gimmick to avoid $38 billion in mandatory cuts to what Obama sought for the Pentagon.

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