This varies from state to state.
Loss leader sales are illegal in certain states. They can be circumvented with certain rebates and coupons depending on the law.
Below is wiki definition:
"A loss leader, or simply a leader, is a product sold at a low price, at or below its market cost to stimulate other sales of more profitable goods or services. Using a loss leader, often a very popular good or service, is a type of sales promotion—a marketing strategy that focuses on pricing strategy. Sometimes "leader" is used as a related term and can mean any popular article, i.e., one sold at a normal price."
[link to www.enotes.com
"In recent years, loss leader pricing has been practiced with considerable success, especially by large national discount retailers. The strategy is not without controversy, however. Indeed, many states have passed laws that severely limitr explicitly forbidelling products below cost.
Lawsuits alleging that some loss leader pricing strategies amount to illegal business practices have increased in recent years, though the plaintiffs have not always been victorious. Opponents of loss leading pricing practices argue that the strategy is basically predatory in nature, designed to ultimately force competitors out of business."