If you ask managers right now what’s the biggest drain on office productivity, they’re likely to answer employees streaming NCAA basketball games. But in a typical week, social-networking websites would certainly be the most popular response.

A survey conducted by St. Louis-based AAIM Employers’ Association of 152 Missouri companies shows that almost 80 percent of them indicate that employee access to social networking websites during working hours is either disallowed or restricted in some way. In Illinois, 80 percent of the 188 companies surveyed said the same thing.

The Missouri survey shows that roughly one-fourth of the companies surveyed reported that access to sites like Facebook, MySpace and LinkedIn is completely blocked from company computers. The vast majority of the Missouri and Illinois businesses say they take disciplinary action against employees who violate a company’s policy on social networking access.

Half of the companies in both states reported using a monitoring system to track websites opened by employees during the work day. And it often falls on the IT department to track this action.