In a surprise move, Square chief operating officer Keith Rabois has resigned from the San Francisco payment company.
The well-respected Silicon Valley investor and former Paypal executive joined Square in August 2010 when the mobile card reading outfit employed 17 engineers and counted just 1000 active merchant users of its technology.
Today, Square employs almost 500 staff and processes over $10 billion annually from a million-strong user base.
Rabois' departure comes at a time of intense competition in the space, with multiple startups mushrooming internationally and deep-pocketed competitors like Intuit, VeriFone and PayPal fighting for market share.
Square has yet to explain the reasons behind Rabois' decision to quit, but tech newswire AllThingsDigital cites unidentified sources who suggest disagreements and tensions with Square founder Jack Dorsey may have been behind for his sudden exit.
Update: In a blog post, Rabois says that he resigned due to accusations of sexual harassment made against him by Steve Berger, a former lover and another Square employee, who has threatened a lawsuit.
In a statement, Square says: "While we have not found evidence to support any claims, Keith exercised poor judegment that ultimately undermined his ability to remain an effective leader at Square. We accepted his resignation."