Justices were skeptical Monday that the case was an exception to other lawsuits against defense contractors, which usually get immunity in such litigation.
Due to processing time, Congress would need to act to ensure military pay Monday or earlier in order to avoid troops' checks being delayed, DFAS confirmed.
Twenty-three states have aligned with the Trump administration's stance that he has authority to bring in the Guard, while 22 back the district's position.
Texas National Guard members are at an Army training center in Illinois, sent despite a lawsuit and vigorous opposition from Democratic elected leaders.