WASHINGTON (AP) — The military’s top leaders are warning Congress that automatic spending cuts looming in March would force the Pentagon to slash operating budgets, weakening the armed forces and possibly forcing furloughs of 800,000 civilian employees.

The Joint Chiefs say in a letter to Congress that the cuts would create a “hollow force” and would require aircraft to be grounded and warships to return to port.

The chiefs said the troops on the front lines would continue to receive the support they need, despite a cut to the Pentagon’s overall budget of more than 7 percent. But those cuts feel more like 20 percent because they’re crammed into the second half of the budget year and pay for uniformed personnel is exempt, as are costs for combat operations.