Be specific about how your job has been diminished. When the director of information technology at a Washington, DC, consulting firm complained after she returned from maternity leave last year that a co-worker had edged in on her turf, she was told she was being silly. "My boss said, 'He just has some good ideas. You should welcome them,'" says the director, who is the mother of a 1-year-old and 5-year-old.
Describe in objective terms how your job has changed. Instead of saying you think a colleague has usurped your responsibilities, for instance, explain that you've been excluded from meetings you used to attend, and if possible, draw a direct link between the change and your compensation. A lower income is the clearest indication that your job isn't comparable, and is difficult to dispute.
Be realistic. You may not be able to have exactly the same job back. In your absence, your boss may have decided to reassign everyone's duties. Or a client may want your maternity leave substitute to finish a project she started when you were out. Suggest that your supervisor give you other assignments to fill the void, and try to set a deadline for that to occur.
But what if your boss fails to respond? If you're covered by the FMLA, you can call the U.S. Department of Labor; if the department believes there's been a violation, it will call your employer. Most such complaints are resolved successfully with just one call.
If you aren't covered by the FMLA or by a similar state law, or you don't want to involve governmental authorities, then you have to decide whether you're willing to threaten to quit. The information-technology director decided that she was. A few months after her leave, she told her supervisor that she didn't want the situation to continue. And it didn't. Her boss quickly looked into the problem and made sure that no one threatened her position. In an economy with the lowest unemployment rate in decades, employees often have more leverage than they think.