Let $𝔐 (z) = ∑_{n=1}^{∞} μ(n)z^n$. We prove that for each root of unity $e(β) = e^{2πiβ}$ there is an a > 0 such that $𝔐 (e(β)r) = Ω((1-r)^{-a})$ as r → 1-. For roots of unity e(l/q) with q ≤ 100 we prove that these omega-estimates are true with a = 1/2. From omega-estimates for 𝔐 (z) we obtain omega-estimates for some finite sums.