The tech sector is having a terrible week, leading the S&P 500 Information Technology sector to close five straight sessions (including last Friday) in the red, and Apple Inc. (AAPL) - Get Report is to blame. 

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Apple shares were down another 1.22% on Friday, adding to the 2.3% decline the stock has experienced this week. Apple's stock has fallen more than 4% year to date. 

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The problem with Apple is that people aren't confident that iPhone sales will be robust enough to keep the bears away. 

Morgan Stanley analyst Katy Huberty wrote last week that she expects Apple to report an in-line March quarter. Huberty lowered Morgan Stanley's June quarter iPhone sales estimate to 34 million from 40.5 million. Wall Street has a consensus estimate of 43 million iPhone sales. 

Taiwan Semiconductor Manufacturing Co. (TSM) - Get Report helped kick start the negative feelings towards the company last week when the Apple supplier issued a headwind warning.

The company said it was facing "weak demand" from mobile customers, forcing it to guide second-quarter revenue between $7.8 billion and $7.9 billion, well below Wall Street's estimates of $8.8 billion.

Taiwan Semiconductor followed up that guidance by saying that it expecys "softening" demand in the high-end smartphone market. 

STMicroelectronics N.V. (STM) - Get Report added to the consternation when the Apple supplier also said that it expected near-term weakness in the global smartphone market. The chipmaker gets about 10% of its annual revenue from Apple. 

Apple is scheduled to report quarterly earnings Tuesday, May 1.