Kit Kat's maker Nestle has been accused of copying Breakout, the 1970s computer game, in a marketing campaign.
Atari, the company behind some of the most popular early video games, has filed a suit alleging Nestle knowingly exploited the game's look and feel.
The advert showed a game similar to Breakout but where the bricks were replaced with single Kit Kat bars.
Nestle said it was aware of the lawsuit and would defend itself "strongly" against the allegations.
'Plain and blatant'
Breakout was created as a successor to "Pong" by Apple founders, Steve Wozniak and Steve Jobs.
In the advert, which is titled "Kit Kat: Breakout", a row of people, of varying ages and appearance, share a sofa and play a video game during their work break. In the game depicted, a primitive paddle moves side-to-side to bounce a ball into a collision with the horizontal bars ranged across the top of the screen.
Atari alleges that the similarity with its original game "is so plain and blatant that Nestle cannot claim to be an 'innocent' infringer".
The legal complaint against Nestle, filed in a San Francisco court on Thursday, claims that the Swiss chocolate maker had hoped to exploit "the special place [Breakout] holds among nostalgic Baby Boomers, Generation X, and even today's Millennial and post-Millennial 'gamers'".
Nestle's spokesperson said: "This is a UK TV advert that ran in 2016. The ad no longer runs and we have no current plans to re-run it.
"We are aware of the lawsuit in the US and will defend ourselves strongly against these allegations."