Stocks are sliding

Stocks are lower in morning trading after closing little changed on Thursday.

Near 9:45 a.m. ET, the Dow was down 118 points, the S&P 500 was down 13 points, and the Nasdaq was down 29 points.

On Friday we got more shaky headlines out of Greece, with Reuters reporting that senior EU officials have officially discussed a "Plan B" in case Greece defaults on its debt.

On Thursday, the IMF withdrew its team negotiating with Greece in Brussels.

In economic data, producer prices saw the biggest monthly gain in five years in May. The Producer Price Index climbed 0.5% month-over-month (versus 0.4% expected) and fell 1.1% year-over-year.

Excluding food and energy, core PPI rose 0.1% from the previous month, in line with expectations, and 0.6% year-over-year (versus 0.9% estimated.)

The University of Michigan's Consumer Sentiment index is due at 10:00 a.m. ET.

Around 1:00 p.m. ET, we'll get the latest count of US oil rigs from Baker Hughes. West Texas Intermediate crude oil is slightly lower at around $60.39 per barrel.

Twitter shares rose 3% in early trading. On Thursday, the company announced that CEO Dick Costolo is stepping down July 1, to be replaced by co-founder Jack Dorsey. It doesn't seem, however, like Wall Street is expecting any drastic changes in the company's direction.