Madonna has shared her support for Britney Spears and compared her conservatorship to slavery.
The Queen of Pop, 62, described the conservatorship, that has been in place since 2008, as a "violation of human rights".
Spears, 39, last month said she had been forced to work, likening the situation to sex trafficking.
Madonna wrote on Instagram: "Give this woman her life back. Slavery was abolished so long ago! Death to the greedy patriarchy that has been doing this to women for centuries.
"This is a violation of human rights! Britney we coming to get you out of jail!"
The message, shared with Madonna's 16.2 million Instagram followers, was written over a picture of her wearing a T-shirt bearing Spears's name.
The two pop superstars have worked together previously.
They collaborated on the 2003 song Me Against The Music and famously shared a kiss during a performance with Christina Aguilera at that year's MTV Video Music Awards.
The #FreeBritney movement has a long list of celebrity supporters. This week socialite Paris Hilton renewed her support for Spears, writing on Instagram: "She is so incredibly brave and an inspiration for speaking her truth."
Cher, Miley Cyrus and Mariah Carey have all voiced their backing of Spears.
