Tricky Urine Drug Test Questions. DON'T NEED ADVICE ON PING. This is a legality issue. Help Please!!?

So I have a questions on drug tests in the work place. My employer never asked for a pee test when I was first hired on, nor was I made to sign an agreement stating that I will submit to random drug tests in the work place. The only reason they are asking me to take a urine test is because we recently received a job where the job site requires anyone who works on this specific job, has to submit to a pee test. I will not be working on any installing or anything of the sort with this job. I want to know, do I have to submit to the urine test? Or is it legal for me to say "No i will not submit to this urine test as you did not ask for one when you employed me" I just need to know some answers. Not to mention they only told me today and the test is supposed to be sometime this week. Is there a certain time period that they have to give me warning? Anyone know anything about this? Thanks for the help