The fashion house pinned the blame for its faux pas on a dodgy translation from Spanish.
"We regret the translation error. The relevant services have been alerted and will make the correction immediately," the company said on its official Twitter account.
The gold chain with the offending caption was priced at €24.99. An online petition organized by French actresses Aissa Maiga and Sonia Rolland and columnist Rokkaya Diallo, entitled "Slavery is not fashion", had on Monday attracted 1,604 signatures.
"This jewellery is meant to make an object of fantasy and fashion out of slavery," they said in the petition addressed to Mango's public relations department.
"Mango is trivializing tragedies... that still today have an impact on millions of human beings across the world," they added.
The caption in French read "collier (necklace) style esclave".
However, in Spanish "esclava", has two meanings: it can refer to a female slave, or to a simple bangle or bracelet.
Vogue was at the centre of a similar Twitter-based scandal last year when it advertised a pair of hooped earrings on its website as "slave earrings."