In the episode, titled "Opposites A-Frack," Mr. Burns gets called into a court hearing for fracking (the process of drilling or injecting millions of gallons of water, sand and chemicals into the ground at high pressure to fracture shale rocks in order to release natural gas).
Mr. Burns winds up falling for the lead assemblywoman prosecuting him in the hearing (Fonda), as she's someone completely different from himself.
"Jane Fonda plays a character named Maxine Lombard, a liberal congress lady that Mr. Burns has a passionate affair with," said executive producer Matt Selman.
"I couldn't believe that Jane Fonda had never done animation or voice over," Selman gushed. "I think she was a little nervous. I think I was more nervous. She was very encouraging of direction and line readings and all the things that famous Oscar-winning actors don't usually ask for. She understood the character and just read every scene perfectly."
In addition to Fonda, The Simpsons' 26th season also boasts guest voices such as Willem Dafoe, Nick Offerman and Sarah Silverman.
The Simpsons airs Sunday nights at 8/7c on FOX. Click here to relive some of the scariest "Treehouse of Horror" segments.