Intel has long allowed all employees to buy stock at reduced prices every six months through their stock participation plan. The last period ended around 2/19. As others have noted, some employees sell their stock through an internal same-day-sale program and pay reduced commissions. Others (most?) hold on to the stock for investment and tax reasons.
What's happened the past few days was probably not significantly driven by employee sales. INTC was priced too high given Intel's stated expectations for the quarter. That, plus the usual market volatility and investor emotion, are driving the price down.
As an aside, those that state with apparent confidence that the price will soon be above 100 or below 70 are speculating, to say the least. Even assuming substantial inaccuracy in Intel's guidance there's no justification for valuations so wildly high or low.