Paula just filed docs -- obtained by TMZ -- alleging Robin and his attorney initiated a bunch of back-channel communication with the Department of Children and Family Services staff ... including a dinner where Robin allegedly wined and dined a case worker. She's even specific, claiming it was an expensive sushi dinner.
According to the docs ... Paula's also accusing Robin of falsely reporting to law enforcement she had kidnapped Julian. She says Robin tampered with the custody order to make it look like she was kidnapping their son.
Paula thinks Robin was trying to embarrass and humiliate her by having cops arrest her in front of Julian.
TMZ broke the story ... DCFS is investigating claims Robin has engaged in excessive physical discipline and he can only see Julian with a court appointed monitor.
Robin's camp tells us Paula's claim is bogus ... yes, he went to Nobu with Julian and the DCFS worker accompanied them because the judge ordered that a monitor be present for all visits. But the rep says the DCFS worker did not eat or even sit at their table. The rep also says Robin only contacted police once last month when Paula had gone MIA for 10 days.