The Dow Jones industrial average fell 100 points at market open on Monday as the U.S. government shutdown entered day 14. Congress must raise the nation's debt ceiling by the Oct. 17 deadline in order to avert an historic debt default.

In company news, Facebook Inc. (NASDAQ:FB) has agreed to acquire Israeli mobile-app maker Onavo for an undisclosed sum.

“As you know, Facebook and other mobile technology leaders recently launched, formalizing Facebook’s commitment to improving access to the Internet for the next 5 billion people -- this is a challenge we’re also passionate about,” Onavo said in a statement.

“We’re excited to join their team and hope to play a critical role in reaching one of’s most significant goals: using data more efficiently, so that more people around the world can connect and share," Guy Rosen, Onavo's co-founder and CEO, said“When the transaction closes, we plan to continue running the Onavo mobile utility apps as a standalone brand. As always, we remain committed to the privacy of people who use our application, and that commitment will not change.”

Shares of Facebook fell 2.30 percent to $47.98 in morning trading.

KGI Securities analyst Ming-Chi Kuo slashed his fourth-quarter shipping estimates for Apple Inc.'s (NASDAQ:AAPL) iPhone 5C by 33 percent. Kuo estimates Apple shipped 11.4 million 5Cs in the September quarter, and also expects 5C sales to be just 10.4 million units for the December quarter, a 10 percent sequential drop.

Shares of Apple edged up 0.33 percent to $494.42.

Ikea, the world's largest furniture retailer, said sales rose 3.1 percent to 27.9 billion euros, or $38 billion, in its fiscal year ended Aug. 31. The Sweden-based retailer cited increasing demand for its furniture and accessories.

“Value for money is increasingly important to our customers -- and our sales development shows that people all over the world appreciate our concept of good quality, well-designed products at low prices,” Ikea's chief executive Peter Agnefjaell said.

Ikea also said that it benefited from market share growth in Russia and China, and that North America showed "significant progress."

The Dow Jones industrial average fell 69.92 points, or 0.46 percent, at 15,167.19. The S&P 500 fell 7.85 points, or 0.46 percent, at 1,695.37. The Nasdaq Composite was down 10.93 points, or 0.29 percent, at 3,780.41.