CP Asymmetry in B_d --> phi K_S: Standard Model Pollution

The difference in the time dependent CP asymmetries between the modes $B --> psi K_S$and$B --> phi K_S$ is a clean signal for physics beyond the Standard Model. This interpretation could fail if there is a large enhancement of the matrix element of the $b-->uubars$ operator between the $B_d$ initial state and the $phi{K}_S$ final state. We argue against this possibility and propose some experimental tests that could shed light on the situation.