Samsung has filed a complaint against Apple with the International Trade Commission (ITC) in an escalating legal battle over the companies’ patents on smartphones and tablets.

According to a document filed with the ITC on Tuesday, Samsung sent a letter to agency secretary James Holbein requesting the commission investigate Apple for patent infringement.

The document did not specify which patents were being contested, but Bloomberg reports that the complaint covers five patents related to the transmission of services over a wireless network; how data packets in high-speed data transmissions are formatted; mobile Web browsing on the handset; the storage and playback of audio; and the use of a touchscreen to view documents.

The ITC has not yet agreed to look into the matter. The agency’s investigations often take 16 to 18 months to complete.

Apple has not yet filed a complaint with the ITC, but such a move seems likely in light of Samsung’s request for an investigation.

The patent fight between the two tech giants began in April, when Apple filed a lawsuit in the U.S. District Court for the Northern District of California alleging that Samsung’s Galaxy products “slavishly copy” Apple’s iPhone and iPad.

Samsung soon fired back with lawsuits of its own filed in Seoul, Korea; Tokyo, Japan, and Manheim, Germany.

Last week, Apple expanded the fight with a complaint against Samsung filed in South Korea, where Samsung has its headquarters.