A federal income tax rule applied to fringe benefits that employers provide their employees. It states that if a company is engaged in multiple lines of business and an employee receives a fringe benefit from a line of the company's business that she does not work in, she must pay taxes on that benefit.

For example, if an individual works for a movie theater and her company also owns an amusement park, if she received free or discounted admission to the amusement park, she would be required to pay taxes on the value of the free ticket or the discount because the IRS would consider this benefit to be income. However, if she saw a movie for free at the theater where she worked, she would generally not have to pay tax on the amount of the free movie ticket because it would not be subject to line of business limitations.