We use mass formulas to construct minimal parabolic Eisenstein congruences for algebraic modular forms on reductive groups compact at infinity. For unitary groups of prime degree, this construction yields Eisenstein congruences for non-endoscopic cuspidal automorphic forms on quasi-split unitary groups.In supplementary sections, we also generalize previous weight 2 Eisenstein congruences for Hilbert modular forms, and prove some special congruence mod p results between cusp forms on U(p).