Operating under a continuing resolution for three months will impact dozens of personnel and construction projects vital to keeping the military operational, Secretary of Defense Jim Mattis is warning top congressional leaders.

In a six-page letter dated Sept. 8 and obtained by Defense News, Mattis wrote to Senate Armed Services Committee Chairman John McCain, R-Ariz., outlining the impacts of a budget extension. The analysis was requested by committee leaders earlier this month, before lawmakers approved a three-month continuing resolution last week.

In the letter, Mattis warns the longer the budget extension, “the greater the consequences for our force.” He said defense officials will realign priorities to ensure that funding shortfalls related to the fiscal 2017 spending continuations do not affect deployed forces, but the military as a whole will still see significant disruptions.

For example, Mattis wrote, training during the next three months “must be re-scoped and scaled to incorporate only mission essential tasks.”

That includes altering an upcoming joint live-fire exercise scheduled to coincide with Marine Corps weapons certifications. Participants now will fire fewer practice rounds and will move ahead “without the benefit of having practiced coordinating joint fires.”

Professional development and training exercises for both military and civilian personnel will be canceled or delayed. Noncritical travel will also be postponed, which could result in “unnecessary turmoil for families.”

Mattis also warned that payments to some outside medical care providers could be delayed, which could lead some private sector offices to cut ties with military patients.

On the equipment side, the Navy will delay the induction of 11 ships, which would push some readiness availabilities into fiscal 2019. The service will also reduce flying hours and steaming days, as well as slow down orders of spare and repair parts.

The Army, meanwhile, will postpone all noncritical maintenance work orders until later in the year, as well as restricting home-station training.

Overall, no new military construction projects can begin, which will have an “inevitable delay in project schedules and potential increased costs,” Mattis warns. That includes 37 Navy projects, 16 Air Force projects and 38 Army projects.

In addition, a short-term budget extension means that no new-start projects can be impacted. The Army appears to be the most impacted in the coming months, with the letter highlighting that there are 18 new-starts and eight production-rate increases that need to be addressed by the end of the year.

At the Defense News Conference on Sept. 6, Pentagon Comptroller David Norquist warned that while the Defense Department could once again survive a short-term continuing resolution, the cumulative effect of multiple budget extensions over the last decade has been “corrosive” for the military.

McCain requested the analysis as a counter to arguments from fellow lawmakers that the short-term budget plan would benefit the military by avoiding a possible shutdown at the end of the month.

He voted against the continuing resolution, which was paired with disaster assistance funds for victims of the recent hurricanes across the southern United States and an extension of the country’s debt ceiling.

Mattis acknowledged that a short-term budget fix does avoid a possible shutdown and may provide an opportunity to undo funding caps currently in place for fiscal 2018. He argued those caps pose an even greater threat to the long-term health of the force.

“Without relief from the (spending) caps, our air, land and sea fleets will continue to erode,” he wrote. “The caps obstruct our path to modernization, and continue to narrow the technical competitive advantage we presently maintain over our adversaries.”

Lawmakers have until mid-December to pass a full-year budget for fiscal 2018, or agree upon another extension.