What conditions is a 1099R not taxable income?

spouse was a member of union local 49 he is now disabled and receives his pension. He is over 591/2 and contributed to his pension fund prior to his disability and now recieves his money. His contributions were made on taxed dollars. I used turbo tax and according to form the total amount didn't move to taxable income I did pay some taxes on this monies simply because I wanted him to share tax liability since I didn't want to be paying all the taxes out of my income. Now the IRS is sending me a CP2000 stating I should have paid taxes on this amount (I reported on line 16a). So what's my argument and is this monies taxable. PLEASE HELP OUT THERE