PK Kemsley is accusing estranged wife Dorit Kemsley of letting their kid's passports expire ... claiming she knew he wanted to take them to Europe this summer but never renewed them before taking off on an extended European vacation herself.

According to new court docs obtained by TMZ, PK's attorney sent Dorit's lawyer a July 7 email alleging both kid's passports had expired despite Dorit allegedly knowing of PK's travel plans with the kids.

The email also claims Dorit traveled to Europe while the children stayed in Florida with her parents and their nanny. PK's attorney says he was never told the children's travel dates, how long they'd be away, what arrangements had been made for them, or when they'd be returning.

PK's attorney further claims he wasn't provided a parenting schedule, leaving him unable to make plans with the children.

According to the docs, PK's legal team demanded confirmation on the status of both passport renewals, along with Dorit's return date and information about the children's care while she was overseas.

As TMZ previously reported, PK recently asked a judge to give him sole authority to sell the couple's Los Angeles mansion, claiming it's on the brink of foreclosure and accusing Dorit of prioritizing an extended European vacation over the family's financial troubles.

Dorit's attorney responded in an email included with the filing, saying she would provide a more detailed response after handling other legal matters.

We've reached out to the Dorit ... so far, no word back.