When Facebook went public, its IPO included a “lockup” agreement that meant some shareholders were required to hold their stock for a predetermined amount of time. For Facebook insiders held to this agreement, that lockup ended today, and as a result, Facebook shares hit their lowest price so far.

Shares were down at least as low as $19.76 at one point.

According to CNNMoney, 22 million shares changed hands in the first ten minutes this morning, and 42 million shares had done so by a half-hour in.

Earlier this week, Business Insider put out a list of potential sellers, which included Peter Thiel, Accel Partners, DST Global Limited, Goldman Sachs, Elevation Partners, Greylock Partners, Mail.ru Group Limited, Mark Pincus, Meritech Capital Partners, Microsoft, Reid Hoffman, and Tiger Global Management.

It’s unclear how many shares from this group of people were actually sold, but there were reportedly over 2 billion shares held by the lockup.

As of the time of this writing, Facebook shares are at $19.95.