In order to safeguard the interests of the STs More effectively, it was proposed to set up a separate National Commission for STs by bifurcating the existing combined National Commission for SCs and STs.  

• This was done by passing the 89th Constitutional Amendment Act of 2003.  
• This Act further amended Article 338 and inserted a new Article 338-A in the Constitution.  
• The separate National Commission for STs came into existence in 2004. 

Source: Laxmikanth