Jennette McCurdy's Feud with Nickelodeon -- It's All About Money

Jennette McCurdy's beef with Nickelodeon is strictly about the almighty dollar ... and how she makes less than her "Sam & Cat" co-star Ariana Grande ... TMZ has learned.

McCurdy was a no-show at the Kids' Choice Awards over the weekend, and took to Twitter to air her grievances, writing, "I was put in an uncomfortable, compromising, unfair situation (many of you have guessed what it is) and I had to look out for me. I chose to not go because sticking up for what is right and what is fair is what my mom taught me is ALWAYS the most important thing."

McCurdy was quick to explain she was talking about Nickelodeon and NOT her racy photo scandal.

Our sources say the source of McCurdy's dissatisfaction is rooted in her paycheck. We're told the pint-sized star is pissed that Grande makes WAY MORE money than her and she's been trying to renegotiate her deal ... so far to no avail.

The show is one of the most popular on the network, but production has been halted and so far a second season has yet to be ordered.