NEW YORK (TheStreet) -- The Federal Reserve'sFederal Open Market Committee meeting and earnings from a number of companies highlight Tuesday for investors.

The Fed holds its two-day meeting starting Tuesday, and economists expect the central bank to begin raising interest rates in September. The Federal Reserve is scheduled to announce its policy decision after the end of the meeting on Wednesday afternoon.

Among those reporting on another busy earnings day are Merck (MRK) - Get Report, Pfizer (PFE) - Get Report, Gilead Sciences (GILD) - Get Report, Ford Motor (F) - Get Report, United Parcel Service (UPS) - Get Report, Twitter (TWTR) - Get Report, DuPont (DD) - Get Report, Panera Bread (PNRA) and Buffalo Wild Wings (BWLD) .

Twitter, scheduled to report after the market closes, is poised to report a year over year rise in both earnings and revenue in its latest quarter. Wall Street estimates call for a profit of 4 cents a share on sales of $481.13 million, according to analysts polled by Thomson Reuters. Investors will likely be digging into the quarterly report, paying close attention to the micro-blogging site's user growth, engagement and monetization. Shares of Twitter have fallen over 9% in the past 52 weeks.

On the economic calendar are the weekly Redbook data on chain store comparable sales, the S&P Case-Shiller home price index, the flash services PMI and the consumer confidence level.