I worked for a large company where I was paid a base pay, but the majority of my income came from a monthly commission based on meeting or exceeding sales goals.
Well, the company always holds back the commission payment until late in the following month (so, the commission I earned for January sales goals, I get paid for at the end of february and so on. )
Well, after having the BEST MONTH EVER in sales in March, I quit the beginning of April. Now the company is saying that they do not have to pay me for the commission I earned in March. They state that I have to be employeed up until the date the the commission is paid out - which mind you would not be until the end of April, and then they would owe me for April, so is it really a never ending viscious cycle?
Can they legally withhold the commission that I earned?

Thanks

It's very possible. You will have to check with the state Dept. of Labor to find out if your state considers earned commissions as vested wages. Many states do not and such payment conditions then are controlled by the comission agreement.