WILL THIS WEAKEN THE GOVERNMENT?
Raja is a member of the DMK, a regional party from Tamil Nadu that helps give the Congress party a majority in parliament.
While Singh's coalition won a strong mandate at the last general election, his government requires the continued support of regional parties such as the DMK to prevent a united opposition scuttling reforms.
Opposition politicians have claimed Singh failed to act against Raja because he feared upsetting his coalition partner.
While Congress needs the support of its coalition allies, the party is mindful that in 1989 it lost a general election partly due to a scandal over gun contracts involving associates of then Prime Minister Rajiv Gandhi who were accused of taking bribes.