Can I be fired for failing a pre-employment drug test if I've already been started?

Last week, I had to take a pre-employment drug test for a parking lot attendant job. I went in on Wednesday(3-30-11) and took the test and the following Thursday and Friday I worked. I've already done my tax paperwork and turned it all in, and I've made great impressions on my employers. Now today (4-4-11)... show more Last week, I had to take a pre-employment drug test for a parking lot attendant job. I went in on Wednesday(3-30-11) and took the test and the following Thursday and Friday I worked. I've already done my tax paperwork and turned it all in, and I've made great impressions on my employers. Now today (4-4-11) I get a phone call from the lab saying that I've failed for THC and it is now up to the employers to decide if they fire me or not. My question is; can they fire me for that if I've already started? I'm 19 and live in Indiana, just saying... Maybe I'm just being hopeful, but not everyone gets fired for this, do they? My boss is a way older man, and we get along fine, he even said that he's going to be the only one seeing me (from the company, at least). It's not like I smoke on the job or show up high... Anyway, I'm just looking for some other thoughts on this. Thanks!
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