We examine the effects of mixing induced light heavy charged lepton neutral currents on the partial wave amplitude for the process l⁺l⁻ →ZZ (withl = e,μ or τ). By imposing the constraints that the amplitude should not exceed the perturbative unitarity limit at high energy (√s = Λ), we obtain bounds on light heavy charged lepton mixing parameter sin²(2θ_L^a) where θ_L^a is the mixing angle of the ordinary charged lepton with its exotic partner. For Λ = 1 TeV, no bound is obtained on sin² (2θ_L^a) form_E < 0.69 TeV. However, sin² (2θ_L^a) ≤ 1.52×10⁻⁵ form_E = 5 TeV, sin² (2θ_L^a) ≤ 2.41 ×10⁻⁷ form_E = 10 TeV. Similarity for Λ = ∞ no bound is obtained on sin² (2θ_L^a) for m_E < 1.97 TeV and sin² (2θ_L^a) ≤ 0.15 form_E = 5 TeV and sin² (2θ_L^a) ≤ 3.88×10^-2 form_E = 10 TeV.