OBC Bill: What it is and why is the opposition supporting it?

This is the last week of parliament's Monsoon Session for the year 2021 and it is highly likely that this week will be a washout too. But Monday was a bit peaceful. The only reason was that the opposition had decided to support the passing of Constitution 127th Amendment bill aka OBC bill. This bill will give the power to states to prepare their own list of other backward castes (OBCs).