The number of American workers who are unhappy on the job is growing and the reasons they are unhappy show a trend.

Rasmussen College did research on the state of the current American workforce and found over 20% of workers are currently unhappy with their jobs.  That percentage represents over 30 million workers.

Their research also found some of the biggest reasons why workers are unhappy.  Over 50% of those who said they were unhappy say they are unhappy because they are underpaid.  Another 30% say they are unhappy because of a lack of advancement opportunities within the company.

John Challenger with outplacement firm Challenger Gray and Christmas says he is not surprised a lack of advancement is cause for unhappiness, "I mean that might just be the permanent state of American workers.  We always feel we are underpaid and under-appreciated."

Challenger says switching companies can be a good way to advance and sometimes it's the only way, "It can be rejuvenating, you've got a fresh start.  You've got people who are looking to you to solve their issues.  They think you have been hired because of your expertise."

Lack of pay and advancement aren't the only reasons for the sullen outlook.  Many workers say they are unhappy because they feel unfulfilled, there is too much stress, or they aren't able to use their education.

Challenger says the long term austerity measures many companies took to survive the recession and down economy have not helped workers or made them feel appreciated.