We exactly compute the partition function for U(2)k × U(2)-k ABJM theory on S3 deformed by mass m and Fayet-Iliopoulos parameter ζ. For k = 1, 2, the partition function has an infinite number of Lee-Yang zeros. For general k, in the decompactification limit the theory exhibits a quantum (first-order) phase transition at m = 2ζ.