WASHINGTON — Defense Secretary Jim Mattis has asked lawmakers not to heap more organizational changes on the Pentagon until has time to implement past rounds.

Mattis sent letters Tuesday to the chairmen and ranking Democrats on the House and Senate Armed Services committees, who are negotiating over their chambers’ versions of the 2018 National Defense Authorization Act. DoD released the letter Thursday.

“Adding further reorganization to ongoing restructuring efforts is more change than we can effectively undertake,” he wrote.

Mattis again voiced opposition to the establishment of a Space Corps, which would be carved out the Air Force—a provision in the House-passed NDAA.

Mattis also opposes Senate-passed provisions to establish a DoD chief management officer and chief information warfare officer as “premature.”

“I ask for your help in allowing the Department time to onboard senior leaders, implement previously mandated changes, and bring needed reforms to the Department,” he said.

Mattis also wants to close excess facilities through the politically unpopular Base Realignment and closure process in 2021, which he says will yield $2 billion in savings annually.

He also opposes an NDAA provision he says will require the U.S. to notify foreign governments before it takes steps to defeat certain cyber threats.

Beyond the matters in the bill, Mattis takes aim at statutory budget caps as his “primary concern.”

“Current caps continue to unnecessarily defer critical maintenance, limit aviation availability, delay modernization, and strain our men and women in uniform,” Mattis writes. “Your continued strong leadership is needed to reverse these challenges.”

Mattis also voiced concerns on various personnel-focused issues, opposing changes to the military health care and supporting Tricare fees that would yield $6 billion. He also supports H-2B visas to supplement the workforce on military construction in Guam.