Inspectors General have a special provision in the law regarding removal or relocation:
> The removal procedure for presidentially appointed IGs is found in Title 5, Section 403(b), which reads in part An Inspector General may be removed from office by the President. If an Inspector General is removed from office or is transferred to another position or location within an establishment, the President shall communicate in writing the substantive rationale, including detailed and case-specific reasons for any such removal or transfer to both Houses of Congress (including the appropriate congressional committees), not later than 30 days before the removal or transfer. Nothing in this subsection shall prohibit a personnel action otherwise authorized by law, other than transfer or removal.
So it's illegal because he didn't notify Congress in advance. That statute was enacted in 2022 specifically to prevent abuses of power such as this.
> The removal procedure for presidentially appointed IGs is found in Title 5, Section 403(b), which reads in part An Inspector General may be removed from office by the President. If an Inspector General is removed from office or is transferred to another position or location within an establishment, the President shall communicate in writing the substantive rationale, including detailed and case-specific reasons for any such removal or transfer to both Houses of Congress (including the appropriate congressional committees), not later than 30 days before the removal or transfer. Nothing in this subsection shall prohibit a personnel action otherwise authorized by law, other than transfer or removal.
So it's illegal because he didn't notify Congress in advance. That statute was enacted in 2022 specifically to prevent abuses of power such as this.