Facebook staffers are likely to flog off millions of shares today as strict rules governing their trade by employees are relaxed.
It constitutes the largest amount of shares to become available since the social networks botched flotation earlier in the year, a period in which many staff and investors have been barred from trading before specific dates.
Many have watched impotently as thousands (and in some cases millions) of pounds have been wiped off their value as the share price tumbled.
Previous windows releasing such shares have led to a glut of stock on the market as staff seek to cash out before the price falls further.
Mark Zuckerberg, will be allowed to sell 504m of his shares, has pledged not to sell until September of next year at the earliest however.
Facebook is currently trading at around $19.97 per share, almost half its launch price of $38.