Kanye West's threatening letter to Kim Kardashian accusing her of exploiting their kids is just a stunt designed to piss off Kim -- one with zero legal bite ... TMZ has learned.

Here's the deal ... on Friday, Ye's purported lawyer, Kathy Johnson, supposedly sent Kim's attorney, Laura Wasser, a cease and desist letter, "concerning the welfare and custody of Mr. West’s minor children: North West, Saint West, Chicago West, and Psalm West."

But we spotted a bunch of red flags pointing to this being a phony correspondence, including the claim Johnson works for a JB Law Firm in Palma, Spain. We've found no record of any such firm in that town ... there is one in the Canary Islands, but a website link for that firm doesn't work, nor does the phone number.

Even if Ye had actually retained Ms. Johnson as his attorney, it would be an odd choice ... unless she's authorized to practice law in California, where he would have to wage the child custody battle with Kim.

A source with direct knowledge tells us Kim's camp is also treating the purported letter as a stunt, and we're told Wasser hasn't received it.

We also contacted Kanye's camp ... and they tell us the letter is a "hoax" and Ye had nothing to do with it.

As you know, Kim and Kanye got divorced in 2021 after 7 years of marriage and 4 kids. As part of their divorce settlement, they have joint custody of the kids and Kanye pays $200K every month in child support.

The alleged cease and desist said Johnson is repping Kanye and his current wife, Bianca Censori ... and it accused Kim of violating Ye's parental rights in several ways. Of course, Bianca would have no legal rights if there were a real custody battle.