Microsoft has said that it has asked US officials to block Apple's attempt to trademark the words "App Store".
Apple submitted an application for the phrase - used for its iPhone, iPad and Macintosh download services - in 2008.
But Microsoft has now told BBC News that it has asked the US Patent and Trademark Office to reject the application.
The company says the term is too generic and competitors should be able to use it.
"An 'app store' is an 'app store'," said Russell Pangborn, Microsoft's associate general counsel. "Like 'shoe store' or 'toy store', it is a generic term that is commonly used by companies, governments and individuals that offer apps."
"The term 'app store' should continue to be available for use by all without fear of reprisal by Apple."
It is not clear why Microsoft has filed papers now, more than a year after the USPTO opened up Apple's original application for opposition.
However the move comes just days after Apple launched its latest App Store, for computer software.
Since the iPhone and other high-end mobile handsets emerged over recent years, downloadable applications - or apps - have become commonplace.
Microsoft runs its own application store for Windows phones, while Google and Nokia also have their own equivalents. Amazon, meanwhile, recently announced plans to open its own retail channel called Amazon Appstore.
Apple did not respond to a request for comment, but it is not the first time the company has found itself on the end of a trademark dispute.
After the iPhone launched in 2007, it emerged that technology rival Cisco owned the trademark, used for a range of internet-based telephone handsets. The two companies eventually settled and have now agreed to share rights over the name.
In addition, the Californian company took nearly 30 years to completely settle its conflict with Apple Corps, the record company founded by the Beatles.