Squatty Potty -- the company known for its toilet stools that help ya go #2 -- believes a rival company's engaged in some pretty crappy behavior online ... so it's suing.
According to docs obtained by TMZ ... Squatty -- which counts "Shark Tank" star Lori Greiner as a big-time investor -- claims a company called Step and Go Health is trying to benefit off its well-known name.
Step and Go sells a similar stool that fits around a toilet "to aid in the elimination process."
SP claims the rival biz refers to its toilet stool as "The Step and Go step" on its website, BUT ... uses the phrase "Squatty Toilet Potty Aid" to get a big push on websites like Walmart.com and HomeDepot.com.
Squatty says this phrasing is nearly identical to its registered trademarks for the popular bathroom product, and believes it's a deliberate move by Step and Go to create confusion with customers.
Translation: This bowl ain't big enough for both of us!
SP's asking a judge to order Step and Go to stop infringing on its trademarks ... and fork over any profits it made while doing so.
Let's face it ... there can only be one #1 in the #2 biz.