Background: Ultralow Q-value β decays are interesting processes to study with potential applications to nuclear β-decay theory and neutrino physics. While a number of potential ultralow Q-value β-decay candidates exist, improved mass measurements are necessary to determine which of these are energetically allowed. Purpose: To perform precise atomic mass measurements of Y89 and La139. Use these new measurements along with the precisely known atomic masses of Sr89 and Ba139 and nuclear energy level data for Y89 and La139 to determine if there could be an ultralow Q-value decay branch in the β decay of Sr89→Y89 or Ba139→La139. Method: High-precision Penning trap mass spectrometry was used to determine the atomic mass of Y89 and La139, from which β-decay Q values for Sr89 and Ba139 were obtained. Results: The Sr89→Y89 and Ba139→La139β-decay Q values were measured to be QSr=1502.20(0.35) keV and QBa=2308.37(0.68) keV. These results were compared to energies of excited states in Y89 at 1507.4(0.1) keV, and in La139 at 2310(19) keV and 2313(1) keV to determine Q values of-5.20(0.37) keV for the potential ultralow β-decay branch of Sr89 and-1.6(19.0) keV and-4.6(1.2) keV for those of Ba139. Conclusion: The potential ultralow Q-value decay branch of Sr89 to the Y89 (3/2-, 1507.4 keV) state is energetically forbidden and has been ruled out. The potential ultralow Q-value decay branch of Ba139 to the 2313 keV state in La139 with unknown Jπ has also been ruled out at the 4σ level, while more precise energy level data is needed for the La139 (1/2+, 2310 keV) state to determine if an ultralow Q-value β-decay branch to this state is energetically allowed.