A federal judge ruled late Friday that the Trump administration violated the law by directing the Federal Emergency Management Agency to halve its workforce.

U.S. District Judge Susan Illston in San Francisco found that the Department of Homeland Security unlawfully usurped FEMA's authority over its own personnel decisions. The ruling came in a case brought by unions representing agency employees.

Illston determined that DHS acted arbitrarily and capriciously when it revoked FEMA's long-standing authority to renew contracts for its Cadre of On-Call Response and Recovery teams, known as CORE. These on-call workers make up a significant portion of FEMA's disaster response staff and are often the first federal personnel deployed after major events such as hurricanes.

The judge noted that FEMA had projected staffing levels of approximately 11,383 employees for the upcoming fiscal year, roughly half of prior levels, without documented reasoning for the reduction. She also criticized officials for using the Signal messaging app on personal devices to discuss the cuts and then deleting the messages.

The decision does not include immediate remedies or penalties. Illston said those issues would be addressed in a separate ruling next month, after parties submit briefings on the scope of relief.

The Trump administration has pursued broad efforts to reduce the size of the federal government during the president's second term. The ruling preserves FEMA's ability to maintain its current staffing structure pending further proceedings.

Illston, an appointee of President Bill Clinton, cited post-Hurricane Katrina reforms that limit DHS from substantially reducing FEMA's authorities and functions. The opinion stated there was no evidence in the record of reasoned decision-making for the shift in policy.