While the economic downturn is prompting many U.S. workers to scrap summer holiday plans, a growing number are planning to bring the office with them on vacation, according to CareerBuilder.

Based on a survey of nearly 7,000 employees nationwide, the Chicago, Ill.-based online recruiting firm estimates that up to a fourth of U.S. workers will maintain contact with their employers over this year's summer holidays, up from 20 percent last year. While some said they felt guilty skipping out on co-workers, others feared losing their jobs.

The survey also found that some 15 percent of employees didn't use all of their days off last year.

Sales reps were the most likely to check in during a vacation, followed by financial services and IT workers, the survey found. In fact, a fifth of IT workers reported that they were required by their employers to maintain contact.

"Unfortunately for some workers, getting away can add unnecessary stress to their lives," said Rosemary Haefner, CareerBuilder's vice president of human resources, in a statement.

According to AAA, fewer workers this year are planning trips during Memorial Day weekend. A recent survey by Newton, Mass.-based Tripadvisor found that the number of Americans planning to use at least half of allotted vacation time this summer was down four percent from last year.