[en] We observed that the superconducting critical temperature T_c(x) of the oxides (R_1-xPr_x)Ba₂Cu₃O_7-y (R=Er, Y, Dy, Gd, Eu) decreases monotonically with increasing Pr concentration x. Using the reduced parameters T_c/T_c(0) and x/x_cr all the experimental data for five studied systems fall onto the theoretical universal curve of Abrikosov and Gor'kov over the reduced Pr concentration regime, x/x_cr<0.6, where x_cr is the critical concentration of Pr for the complete suppression of superconductivity and T_c(0) is the T_c for undoped material. The consistency of these results suggests a pair-breaking mechanism which plays a role in depressing superconductivity in these high T_c oxides