Americans continue to grow increasingly unhappy at work, continuing a long-term trend that should be a red flag to employers, according to a report released Tuesday by The Conference Board.

The survey of 5,000 U.S. households, conducted for the New York-based Conference Board by TNS, found that only 45 percent of those surveyed say they are satisfied with their jobs. That figure is down from 61.1 percent in 1987, the first year that the survey was conducted, and from 52.1 percent in 2005.

“While one in 10 Americans is now unemployed, their working compatriots of all ages and incomes continue to grow increasingly unhappy,” said Lynn Franco, director of consumer research at The Conference Board. “Through both economic boom and bust during the past two decades, our job satisfaction numbers have shown a consistent downward trend.”

Fewer Americans are satisfied with all aspects of their employment, and no age or income group is immune. In fact, the youngest cohort of employees (those currently under age 25) expresses the highest level of dissatisfaction ever recorded by the survey for that age group, the report said.

“These numbers do not bode well given the multi-generational dynamics of the labor force,” said Linda Barrington, a managing director at The Conference Board. “The newest federal statistics show that baby boomers will compose a quarter of the U.S. workforce in eight years, and since 1987 we’ve watched them increasingly losing faith in the workplace.”

The drop in job satisfaction between 1987 and 2009 covers all categories in the survey, from interest in work (down 18.9 percentage points) to job security (down 17.5 percentage points), and crosses all four of the key drivers of employee engagement: job design, organizational health, managerial quality and extrinsic rewards.

For more information, see conference-board.org/utilities/pressDetail.cfm?press_ID=3820.