The invention relates to a method for producing a transverse sealing seam in a tubular bag (6) having a longitudinal sealing seam (5), wherein the tubular bag (6) is passed through between a sonotrode (1) and an anvil (2) and, in order to produce the transverse sealing seam, the sonotrode (1) and the anvil (2) are moved toward each other so that a welding force is applied to the tubular bag (6). In order to provide a method and transverse sealing device with which the stated disadvantages can be overcome at least reduced, the longitudinal sealing seam (5) is moved through a gap (8, 7′) formed in the sonotrode (1) or the counter tool (2) at least during the application of the welding force.