Washington (CNN) A top aide to White House chief of staff Mick Mulvaney, Robert Blair, has refused to testify in the House impeachment inquiry of President Donald Trump after the White House directed him not to appear for his scheduled deposition, his attorney told CNN.

The House committees investigating Trump had scheduled Blair's deposition for Monday.

"Mr. Blair is caught between the assertions of legal duty by two coequal branches of government, a conflict which he cannot resolve," Blair's attorney Whit Ellerman told CNN on Saturday.

"In light of the clear direction he has been given by the executive branch, Mr. Blair has respectfully declined to appear and testify. Nevertheless, he will fulfill all his legal duties once that conflict is appropriately resolved."