a machine for forming stacks of bags from a web of synthetic thermoplastic material has feeding rollers for feeding the web to welding jaws which form transverse welds in the web . there is a first motor for operating the feeding rollers and a second motor for operating the welding jaws . a central processing unit controls operation of the respective motors and includes a controller for the first motor for operating the first motor for an increased time and at a reduced speed during feeding of a leading bag in a stack as compared with the time and speed of operation of the first motor during feeding of remaining bags in the stack . this facilitates the removal of a previously formed stack of bags from a machine .