Microsoft, HTC, Nokia, and Sony Ericsson have filed formal applications for a declaration of invalidity against Apple's trademarks for "App Store" and "Appstore" with the Community Trade Mark office in Europe.

The four companies join Amazon, which filed a similar complaint in Europe against Apple in mid-April. All seek to get Apple's two European trademarks invalidated, saying the moniker is too generic.

"Today's filings by HTC, Nokia, Sony Ericsson, and Microsoft, like Amazon's recent action, demonstrate the breadth of opposition to Apple's unsupportable claim of exclusivity," a Microsoft representative said in a statement. "'App store,' like 'toy store' or 'book store,' is a generic term that should continue to be available for everyone to use for stores that sell apps."

The new claims specifically call out Apple CEO Steve Jobs for referring to competing applications markets on another phone platform--specifically Google's Android--as "App Stores." The claims also highlight the fact that several other retailers make use of the term, including Shopify, Sendmail, and DirectTV.

Apple did not immediately respond to a request for comment.

This move follows a similar legal effort in the U.S. by Microsoft in January. Apple's attempts to trademark the term "App Store" with the U.S. Patent and Trademark Office back in 2008 resulted in Microsoft launching a legal battle, complete with both sides obtaining linguists, and other language experts to argue whether the two words were synonymous with Apple's App Store, or mobile application stores in general.

Why are these companies so worried For one thing, Apple's already gotten litigious on the matter. Back in March, Apple sued Amazon over its use of the "Appstore" in the title of its mobile application store for Android devices. At the time, an Apple representative said Amazon's word choice could "confuse and mislead customers." Amazon responded by countersuing, and followed a similar party line to Microsoft, saying Apple's claims were too generic.

Updated at 10:15 p.m. to clarify that Apple already has the trademarks for "Appstore" and "App Store" in Europe.