Benoforia, sorry I thought you already had a work permit
 But I must have been confused with AleMagar! Your friend is right, it's easiest for an employer to file for you (although I think you can also get a lawyer to file on your behalf if you're a consultant). Hopefully they can get you one, it can be hard for companies to obtain visas for foreigners. (You might need to pay for a bond though...your employer should ask their contacts in immigration.)
Once you have your work permit, that gives you permission to work in TNT...but only that. (I think other countries call the work permit "visas"). If you have plans to ever leave and come back to TNT (i.e. if you go on vacation) while you have a work permit, you need to also get a multiple entry visa.Â
You'd file for this on your own by showing your work permit to the immigration dept. This way you can go and come without having to pay the visa waiver fee (60 USD) at the airport every time you enter the country. If you have no plans to leave TNT while working here, the multiple entry visa isn't necessary.
@Sanmig, and @AleMagar try emailing the TNT embassy in NYC (passports@ttcgny.com). They may be able to help you out if you do need a visa.