While Williams has previously held the world number 1 rank, she is now 183rd - a result of playing just three professional events in the past year due to her recent pregnancy.
The 36-year-old American gave birth to a daughter last September and was off the tour for more than a year.
In May, French Open officials declined to grant her a seed, touching off a debate about how the sport should treat its ranked players who return to the game following childbirth.
The All England Club usually follows the women's WTA world rankings, but reserves the right to change seedings - the top 32 players in the draw.
Williams has been "seeded" in the starting lineup of the tournament, which means she has to play opening matches against lower-ranked opponents, and has a better shot at the title.
The Wimbledon seedings for the men are determined by the ATP ranking list of the top 32 players, but can be rearranged based on an individual's grass-court record.
The US Open Grand Slam in NY has said it will update its seeding policy to take into account a player returning from a pregnancy. "If they put her in front of me then I will lose my spot that I am supposed to have", said Cibulkova.
The draw for Wimbledon is Friday; play begins Monday.
Typically, tournament seeding mirrors world rankings. "I don't think it's the right thing to do", Cibulkova told BBC before the ruling.
"Why should I not be seeded if I have the right to be?" asked Cibulkova after losing to Angelique Kerber at Eastbourne. She pulled out of that tournament in the fourth round because of an injury. Caroline Wozniacki, John McEnroe and USTA president Katrina Adams have spoken out in support of Williams. The slide resulted from a near year-long absence triggered by a freak injury, in which she stepped on broken glass and later developed blood clots in her lungs following her 2010 Wimbledon championship.
Business Insider contacted the All England Club to find out their justification for the seeding, but is yet to receive a response.