Ok, now that I’ve finished reading through all of the posts- eek, again. I am concerned. Right now I really need to stick it out for a while, but you’re all correct about the red flags.
That’s very true. But now there should be massive amounts of alarm bells going off in your head, and I’d (if I were you) pay far more attention to the helpful advice upthread and ignore the snark.
Just to make one thing clear, the self-employment tax they’ve talked about is the employer’s share of SS/FICA, which will be 7.65% of your income and which you will be required to pay in your next income tax return. And it has nothing to do with your actual income tax.
So if you decide to keep this job, immediately start shoving 7.65% of your income into a savings account to cover that.
If I were you, I would continue the job search. Keep this job for income (and if you don’t get paid on time, in full, on your first payday, don’t keep the job–walk), but continue to look for a better place to work. It sounds iffy to me too.
The agency is on the paychecks (and I’m only paying 6.2% for SS and 1.45% for medicare so I assume my employer pays the agency who then pays for half of my FICA taxes), but my badge ID says ‘contractor’.
Yup, you’re an employee of the temp agency, and they’re doing what they should be doing. It’s all good.
Jesus - you’re getting screwed all over the place Alice 
Personally, I think I would start stashing the 7.6% as mentioned above and spend every spare moment you have looking for a new job. This sounds *REALLY[.i] hinkey.
I wish this was BBQ Pit so I could rant about IRS, its rules about Forms 1099, etc,. and at employer delight at evading benefits. I also was thoroughly screwed before becoming “Mad as Hell, not taking it anymore” and retiring to a contented life overseas, bemused at the mass hypnosis of Americans.
If it makes you feel any better, stringent IRS rules do not apply to the Successful Americans Who Are Better Than You™ . I recall winning a lawsuit (against an employer under whom I was an abused contractor), and being walked to the bank by his secretary so I could hand her a large stack of banknotes for my lawyer (a Fundie Christian, no less) without any paper trail.
(I see I still retain enough anger about these incidents to be abusive. If necessary, I hope Mods will move my Post to BBQ Pit.)