Microsoft continues to hammer Apple by launching a new promo that gives Apple's MacBook Air owners up to $650 in store credit for trading in certain models of their tablets for its new, Intel-based Surface Pro 3.

The new promotion will run from June 20 to July 31, 2014, or while supplies last. It requires users to bring their MacBook Airs into select Microsoft retail stores in the U.S., Puerto Rico and Canada.  The trade-in isn't valid online, however.

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The thin Surface Pro 3 offers a 12-inch display, Core i3, i5, or i7 processors and a new Surface Pen stylus with 256 levels of pressure sensitivity. It competes directly against Apple's ultra thin MacBook Air, hence the reason for Microsoft's new trade-in promo.

The entry-level Core i3 Surface Pro 3 sells for $799.  Improved versions with a Core i5 and Core i7 processor are priced from $999 and $1949.

With the discount for turning in a MacBook Air, customers could wind up paying only $150 for an entry-level Surface Pro 3 model.

There is a catch to Microsoft's promo, however.

The company says that to be eligible for trade-in, the device must power on to be considered working.

"Water-damaged devices and devices with cracked screens are not considered working devices for purposes of this offer," Microsoft said.

All trade-ins are final and provided as part of the "Recycle for Rewards program" from CExchange LLC. The trade-in is limited to one trade-in per purchase.

To get the maximum value of $650, a customer has to apply the store credit toward the purchase of a Surface Pro 3. It is not clear how much Microsoft is offering for older models at this time.

There's also no information on the Microsoft store sites that will trade-in the MacBook Airs.

The Surface Pro 3 is a Windows 8.1 tablet announced on May 20, 2014. Its first models were released on June 20 in the U.S. and Canada.

The Surface Pro 3 comes with an improved, multi-stage kickstand. Among its new accessories are a redesigned type cover and a battery-powered Bluetooth pen. Battery life comes to nine hours of web browsing, and can last up to one year in sleep mode.

TagsMacbook Air, Surface Pro 3, Macbook Air Surface Pro 3 trade-in