Like the last post, I to think it's 20 lbs. Just take it really easy during the 1st trimester. BUT the one thing my ob told me was don't do anything your body is not use to doing. If you have been working for a while and your body is use to it then just take it easy, quit as soon as you feel uncomfortable and make sure to talk it over w/your dr for what is best for your pregnancy. I felt better just keeping on AND it will help you have a easier labor. You don't want to take it so easy you just sit around and gain a bunch of weight.
I think that 20 pounds is supposed to be the limit BUT I am not 100% sure...our cat was like 20lbs and I told the doctor that when I was prego and she said that was fine...However I am under the impression that your work should make accommodations for you if you can't lift the weight. There is something called a 504 plan which allows for accommodation in schools and workplaces. I would discuss your concerns with them and see if they accommodate you before you quit your job...you will probably need this money to provide for your baby when it comes so it would be best to stick with your job and save some money if you can. I am not a doctor so I really don't have the answer but I would really think twice before quitting my job especially in this economy!