CHICAGO -- Research In Motion is asking a US court to invalidate a previous agreement with Motorola under which the firms agreed not to recruit each others' employees.

In a suit filed in a Chicago court, RIM, the world's top maker of smartphones, asserts improper and unfair competitive practices on the part of Motorola is preventing the hiring of perhaps thousands of laid-off workers. The terminated Motorola workers had signed nondisclosure agreements which in effect would make them unhirable by competitors.

The legal wrangling dates to last February, when the competitors signed a pact agreeing to not solicit each other's employees. In the suit, RIM claims that deal expired in August, and is asking the court to invalidate the pact and award unspecified damages.

RIM, which has been growing on the strength of its popular Blackberry and Storm smartphones, said in the suit, "RIM entities continue to grow and hire new employees within the United States and globally against a backdrop of recent public announcements by Motorola that it has and will continue to make massive layoffs."