Story highlights The defense secretary warned about harm to training, maintenance and personnel

Congress passed a three-month continuing resolution to keep the government funded

(CNN) Defense Secretary James Mattis is warning Congress that a long-term continuing resolution to fund the government will lead to irrecoverable lost training time, delayed ship maintenance and critical personnel gaps.

In a letter to defense committee leaders obtained by CNN, Mattis detailed the effects of a continuing resolution, which Congress frequently uses to keep the government funded at the previous year's spending levels.

President Donald Trump signed a three-month CR into law last week as part of a package that included aid for Hurricane Harvey relief and a three-month extension of the debt ceiling.

But the military objects to CRs because they aren't allowed to start new programs and are restricted in moving money between spending accounts.

"Long-term CRs impact the readiness of our forces and their equipment at a time when security threats are extraordinarily high," Mattis wrote. "The longer the CR, the greater the consequences for our force."

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