A search for heavy neutral gauge bosons (Z ') decaying into a pair of tau leptons is performed in proton-proton collisions at root s = 13 TeV at the CERN LHC. The data were collected with the CMS detector and correspond to an integrated luminosity of 138 fb(-1). The observations are found to be in agreement with the expectation from standard model processes. Limits at 95% confidence level are set on the product of the Z ' production cross section and its branching fraction to tau lepton pairs for a range of Z ' boson masses. For a narrow resonance in the sequential standard model scenario, a Z ' boson with a mass below 3.5 TeV is excluded. This is the most stringent limit to date from this type of search.