Amazon.com shares dropped to levels not seen since March yesterday on concern that big spending and aggressive pricing by the No. 1 Internet retailer will hit profit during the crucial holiday season and well into next year.

The shares slipped 30 cents to close at $180.21, but touched $170.25 earlier in the day.

That put the stock at the lowest level since late March and left it in negative territory for the year.

As recently as mid-October, Amazon’s shares hit a record $246.71, up more than 35 percent for the year to date.

Since then, Amazon has launched its Kindle Fire tablet at a $199 price point, which IHS iSuppli and other computer industry analysis firms estimate is close to cost, putting profit under pressure in the short term.