As of 12:45 p.m. EDT, the Dow Jones Industrial Average (INDEX: ^DJI) is currently trading slightly lower for the day. At 13,304, the index is down 2.01 points, or 0.02%. Fifteen of the 30 companies which make up the Dow are lower on the day. The three biggest losers today are Intel (Nasdaq: INTC), Boeing (NYSE: BA), and 3M (NYSE: MMM), trading lower by 3.3%, 1.76%, and 1.47% respectively.

Why?
Last Friday, Intel cut both its revenue guidance and its expected margins. Shares of the chip makers traded lower in the morning but closed Friday slightly higher for the day. Today, following the company's forecasts, Japanese brokerage Nomura Holdings stated concerns with notebook shipments and decelerating global PC demand. Fool tech analyst Evan Nui also has similar concerns with Intel, as its PC business makes up almost two-thirds of the company's revenue.

Aircraft maker Boeing is also feeling the heat today. Much like its airliner clients, Boeing has found itself in a tough negotiation with the union. In Seattle, 23,000 engineers with a contract due to expire Oct. 6 can't come to an agreement with Boeing over a number of issues. The largest disagreement is related to switching workers to a 401(k)-style retirement program, rather than a pension. With the deadline fast approaching, investors are worried, which is always the case when huge unknowns loom.

Lastly, conglomerate 3M is shedding weight today after announcing it will unveil a new coating for solar panels that will help keep the outer surface cleaner for a longer period of time. Cleaner panels increase the wattage produced by each cell and lower maintenance costs. The product has been lab- and field-tested, and the company believes customers will experience promised results in real-world conditions. After only half the trading day had passed, more than 3.2 million shares had traded hands, while the average volume is only 2.7 million. With increased volume and no bad news pertaining to the company, there is a strong chance that the stock price decline is being caused by a large institutional investor dumping shares.

Moving forward
3M shareholders have nothing to worry about today and should sit tight. Boeing investors should keep a close eye on the union negotiations during the next few weeks. A strike will really hurt future revenue and, ultimately, the share price. A number of analysts are now showing concern over Intel's future, and investors should start deciding whether to buy, sell, or hold. Check out this free premium research report, which will help you make the best decision on Intel. Click here.