Former first lady Hillary Clinton's appointment as US Secretary of State has been challenged by an American diplomat,who has filed a lawsuit terming it as 'unconstitutional'. The lawsuit has been filed on Thursday by 'Judicial Watch' ¿ a Washington-based watchdog group on behalf of David C Rodearmel,a US diplomat working in the State Department. The lawsuit maintains that Clinton is constitutionally ineligible for the post and as such Rodearmel cannot be forced to serve under her,as it would violate the oath he took as a Foreign Service Officer in 1991,said a statement issued by the Judicial Watch. Under the Emoluments or Ineligibility clause of the US Constitution,the lawsuit argues that no member of Congress can be appointed to a civilian position within the US government if the emoluments of the position,such as the salary or benefits paid to whoever occupies the office,increased during the term for which the Senator or Representative was elected. The lawsuit argues that the emoluments of the Secretary of State increased three times during her term as the US Senator. That term,which began on January 4,2007,does not expire until January 2013,regardless of Clinton's recent resignation. The Congress attempted to evade this clear constitutional prohibition with a so-called Saxbe fix last month,reducing the Secretary of State's salary to the level in effect on January 1,2007,the lawsuit charged. The lawsuit,however,points out that the legislation does not and cannot change the historical fact that the 'compensation and other emoluments' of the office of Secretary of State increased during Clinton's tenure in the Senate. This historic legal challenge should remind politicians of both parties that the US Constitution is not to be trifled with, said Judicial Watch president Tom Fitton. In a statement,Rodearmel said this is not a partisan,political or personal issue. I am bringing suit to finally resolve this issue and to seek compliance with the manifest tenor of the Constitution, he said.