  Two anomalously weak transitions within the $2 ^3{\rm S}_1~-~3 ^3{\rm P}_J$
manifolds in $^3$He have been identified. Their transition strengths are
measured to be 1,000 times weaker than that of the strongest transition in the
same group. This dramatic suppression of transition strengths is due to the
dominance of the hyperfine interaction over the fine structure interaction. An
alternative selection rule based on \textit{IS}-coupling (where the nuclear
spin is first coupled to the total electron spin) is proposed. This provides
qualitative understanding of the transition strengths. It is shown that the
small deviations from the \textit{IS}-coupling model are fully accounted for by
an exact diagonalization of the strongly interacting states.
