Just when you thought that the American worker could not get squeezed for any more juice, major retailers have come up with a new cost-savings innovation to apply more pressure on their workforce. Indeed, staffing is the latest area where big retailers like Wal-Mart, Target, and Payless hope to wring out a few pennies with new operational efficiencies.

Mind you, Wal-Mart and its kin already have been blasted for paying low wages, being miserly with health benefits, and reticent to pay their workers overtime. So how could matters get worse for their employees?

Major features in the Wall Street Journal and the San Francisco Chronicle this week reveal that new computerized scheduling systems will move many American workers from a predictable work shift to staffing based on the number of customers in a store at any given time. The system will allow managers to start the business day with a few employees on hand, then bring in "on call" workers when business picks up during the course of the day. Once commerce lags, the manager can send workers home until further notice. In short, it matches staffing to more closely match customer demand.

It's easy to see how this practice could increase productivity and, hence, operational profitability. But consider the plight of workers who no longer can budget their expenses for a week, or arrange for baby sitting for their kids if called into work, or hold a second job that might help them make ends meet. They are essentially at the beck and call of their boss on a daily basis. Rather than work, say, four 8-hour shifts per week, a worker might work two hours one day, six another, and three on a subsequent day. The practice will force a large slice of American workers into low-paid, part-time jobs.

"The whole point is workers were a fixed cost, now they're a variable cost," Kenneth Dalto, a management consultant told the Wall Street Journal. "Is it good for workers?" he added. "Probably not."

I don't know why Dalto had to throw the word "probably" into his assessment. It's clearly a nightmare scenario for workers who will be pressured to be available at the drop of a hat. It gives "flex time" a whole new meaning. It used to mean that workers could arrange their work to fit their personal demands. It now means that workers will arrange their lives to meet the demands of commerce.

Wal-Mart now asks its hourly employees to fill out a schedule of their availability, and encourages them to include a weekend window "if at all possible." This "personal availability form states: "Limiting your personal availability may restrict the number of hours you are scheduled." The obvious implication is that the less flexible you are, you may find yourself in the manager's dog house and fall to the bottom of his call list.

The San Francisco Chronicle reports that some longtime workers, who have reached higher pay scales, fear that managers are using the system to pressure them to quit their jobs. After working 16 years at a Wal-Mart in Hastings, Minnesota, Karen Nelson says managers told her she had to be opening to working nights and weekends. When she refused, her manager told her, "[I can] get two two people for what I pay [you]." Her hours were cut, though restored again after she filed a complaint.

While retailers can defend the new staffing policies by hiding behind improved customer service - workers will be present when the customers most need them - the truth of the matter is that it places an unfair burden on workers. Just how far can we squeeze the worker? It looks like mammoth American retail chains are willing to test that proposition.