If you seek the temp. residency through work, then your employer must be registered in immigraions under the "registro nacional único de requirentes de extranjeros". They also need to create a contract for you.
To work u just need a C.U.I.L. but if you change jobs, the new employer must be registered in immigrations.
If they dont register, the 3 years you need to become a permanent resident through a work visa, will not accumulate. You also need to save all you pay stubs because you need to have pay stub for all 36 months.
So if you plan to stick to your job, then its all good, but if you plan to switch remember that the employer must register at immigration so that your work visa can continue to be renewed every year.