Fighting with my SO over the kids!!

My husband and I have this monthly battle (and I mean battle!!) over the kids. He is their step father and it seems like while my son (6) and him get along great 90% of the time, my daughter (3 almost 4) fight constantly!! He's airways talking about how she hates him. He won't pick them up from anywhere because "they'd rather be with you anyhow. Sis hates me." He used to play all the time with her and doesn't anymore. He says I'm yup lax with her and never punish her. I need to "drop the hammer" and "be more strict with her". He even tells me "if she wasn't so spoiled she wouldn't be such a brat." I'm giving up. I can't keep having this argument and I feel like my only option is to give into "his way" and be more like a damn dictator just to stop the fighting. I've told him a million times my point of view and how I feel about it and he always says he understands and will take it into consideration, yet nothing changes...

What do I do?