"While we're very optimistic about the new products in our pipeline, we still face challenges," the newspaper quoted the email as saying.
"Our costs are too high, we're operating in markets where we're not competitive and we're losing money."
The layoffs will affect workers in the United States, China and India, according to the Journal.
Motorola could not immediately be reached for comment, but the Journal quoted a spokesman as saying the cuts are "obviously very hard for the employees concerned, and we are committed to helping them through this difficult transition."
Google completed its $12.5 billion purchase of the Motorola unit -- which makes smartphones and other devices -- last May, eyeing both its mobile phone line, which uses Google's Android platform, and some 17,000 valuable patents.
Motorola Mobility was created in 2011 when US-based Motorola Inc split the company into a mobile devices unit and a government and public safety division known as Motorola Solutions.