The holiday season is arriving, and that means online shopping. And whether or not you expect it--or even allow it--your employees may be doing some of their bargain-hunting during work hours.

According to a new study, 50 percent of your employees will shop online for holiday gifts while at work. And of those employees, 42 percent will spend at least an hour per day doing so. The study, conducted by Harris Poll on behalf of CareerBuilder, polled more than 2,000 human resource managers and 3,000 employees in August and early September.

So is on-the-job holiday shopping a relatively harmless diversion, or a serious problem you need to deal with? The survey found that 12 percent of employers have fired an employee for holiday shopping online while at work, while 28 percent say they've fired employees for using the Internet for "non-work-related activity."

If you're concerned about your workers shopping, first make sure you're not doing it yourself. Set the precedent so they know the behavior they should model. Many employers go further than that, the study found. More than a third said they monitor employees' Web traffic, while 56 percent said their company blocks specific websites. 

If you have a holiday shopping policy in place already, make sure everyone knows what it is and what the consequences are for violating it. If not, figure out the best policy for you and your employees, whether it's allowing online shopping during lunch and other breaks, or forbidding it completely--and again, spell out the consequences explicitly.