The Weinberg operator is a well-known solution to explain light neutrino masses. This operator violates lepton number and can provide non-equilibrium dynamics in the early Universe due to the suppression of tiny neutrino masses. A lot of underlying symmetries proposed in the lepton sector strongly motivate the existence of phase transitions at high scale. During the phase transition, the coupling of the Weinberg operator may be time-dependent, and the lepton asymmetry is generated by the interference of Weinberg operators at different times. This mechanism does not require any explicit new particles beyond the standard model or seesaw models.