The US whistleblower accused the reality TV star of selling out the transgender movement this year.
Caitlyn Jenner has become one of the most high profile transgender advocates since revealing her transition earlier this year.
Although Jenner has won a legion of fans since coming out – with many praising her bravery – others have criticised the millionaire for falsely representing many in the trans community.
Chelsea Manning echoed these sentiments on Christmas Eve, when she accused Jenner of stealing the trans movement for her own gains.
“In 2015 @Caitlyn_Jenner was the grinch who stole (& sold out) the trans movement,” she tweeted.
“All I want 4 Xmas is Universal Trans Lib. #ChristmasEve2015.”
Jenner also faced a backlash from the trans community after claiming it’s “easier” if you don’t look like “a man in a dress” earlier this month.
It’s not the first time she has shocked LGBT fans – earlier this year admitting that she used to oppose equal marriage, before publicly coming out as transgender.
Explaining that she had changed her mind on the issue, she said: “If the word ‘marriage’ is really, really that important to you, I can go with it.”
Private Manning, who announced her transition to female in 2013, is currently imprisoned in Fort Leavenworth military prison after leaking details of classified documents via WikiLeaks.
The Military seemingly gave the go-ahead to treatment earlier this year – but Manning is suing for her right to transition, as the US Military has continued to force her to present as male, including forcibly shaving her head.
The trans prisoner uses her vast support network to help raise awareness of her case and even write articles from prison.
In August, she faced trial for number of ‘infractions’ – including “medicine misuse” for owning a tube of expired toothpaste, and “possession of prohibited property” for reading material including a copy of Vanity Fair featuring Jenner on the cover.