What may be the nation’s biggest lawsuit is based on one of its longest-running debates: Are women paid less than men in comparable jobs with all the many factors of experience, years at a specific job, performance, etc., factored in? The Wal-Mart case could serve as the means to arguing and perhaps even finding a conclusion to that question.

The General Accounting Office last year concluded that a significant difference in pay existed between men and women even when several factors were considered. The complaint against Wal-Mart is that it pays women 5 to 15 percent less than men and fails to promote them at a similar pace. These are seemingly simple charges, ones that may be proved statistically, but will nonetheless grow complicated once enough lawyers apply their ingenuity. Instead, a jury’s decision may be swayed by anecdote.

For instance, Stephanie Odle, an assistant store manager at a Wal-Mart supermarket in Riverside, Calif., recently told The New York Times that a male assistant manager in the store was making $60,000 a year, $23,000 more than she was earning. She said, “When I went to the district manager, he first goes, ‘Stephanie, that assistant manager has two children to support.’ I told him, ‘I’m a single mother, and I have a 6-year-old child to support.'”

Another complainant was Betty Dukes, a 54-year-old Pittsburg, Calif., woman. She called The Times from her lawyer’s office as the lead plaintiff in a lawsuit accusing Wal-Mart of discriminating against women. She has worked 10 years for the company and is still a store greeter, despite repeated efforts to advance. Repeatedly, she said, men were promoted to the jobs she wanted. She said she was reprimanded for minor infractions like returning late from a break, while men were not.

She started as a part-time cashier at $5 an hour. She now makes $12.53 after a raise a year ago.

The two employees are among dozens who have brought suit against Wal-Mart. Last week, they won an important round when Judge Martin J. Jenkins of the United States District Court in San Francisco ruled that one of the cases could proceed as a class action covering as many as 1.6 million current and former employees. The suit says that only 33 percent of Wal-Mart’s managers are women, while 65 percent of its hourly employees are women. It asks for back pay and changes in personnel policies. The company disputes the complaints and says that a class action is not justified. It says it will appeal the ruling.

Companies often settle such cases rather than letting them drag on and harm their reputation and their stock. Not that it is a reason to take the case to court, but its scale makes it a fascinating study of corporate attitudes and may answer the long-debated question of wage fairness. Or at least start a few hot debates along the way.