Take a look at the typical supply and demand model on the left for your typical labor market. Here S represents the supply of labor, people like you and me who apply for, and work at jobs to receive a salary. The higher the salary offered, the more people are willing to work, either by getting a job at all, or their willingness to work more hours. This is why the labor supply curve (the S curve) is upward sloping. The curve D represents demand for labor. This would be corporations and businesses that need labor as an input in their production process. These businesses are willing to higher more labor if they can get it for a cheaper price, which is why the D curve slopes down.
But what happens in this labor market when an income tax is introduced?
Lets introduce a tax on labor supply (which is us the workers) and see how it affects the market. Consider the graph below:
First consider point A, our market equilibrium. Here we have Q* amount of labor working, and receiving a salary S*. When the tax is imposed and S shifts up, it now interacts with the D curve in a different spot, causing a change in equilibrium salary and quantity. The new equilibrium quantity at Qt is less than it was before, because the real cost of salaries to firms has gone up. The new equilibrium at point B results in a higher salary paid by employers which is Sp. However, because of the tax, labor does not actually receive this salary, they instead receive salary Sr which is equal to Sp (the amount paid by businesses) minus the tax.
So an income tax results in a lower quantity of labor being supplied to the market (people either stop working, or work less hours), and a higher salary paid by employers and a lower salary received by employees. An income tax has negative effects on an economy but unfortunately is needed to fund government services such as schools, roads, and the military. But there are some things we can to to reduce the tax burden in our personal lives so we do not feel the pinch as much.
For example, there are tax software packages available to assist with filing your taxes to make sure you get all of the deductions and credits you qualify for. My favorite is turbotax because of its ease of use, and it remembers my information from year to year. You should also consult the IRS website, which maintains a useful tax FAQ. Finally, if you are behind on your taxes, you could potentially face heavy fines and penalties. If you missed the deadline last year, it is a good idea to file a tax extension form for 2010 in order to get back into good standing with the IRS. My good friend didn't pay taxes one year because of a study abroad trip only to have the IRS take money from his bank account (including fees and interest) five years later when he wasn't expecting it.