Question regarding Worker's Comp?

I have a client that broke his leg on the job in 2006. His union hall paid him $5600 in worker's comp wages. I prepared his taxes but I did not have a W2 at the time for the $5600. I told him that worker's compensation is not taxable.

He just got a CP2000 stating he neglected to include the $5600 on his return. I called the IRS and told them these were worker's comp wages. They agreed that the wages were not taxable but they said my client would need to have the employer correct the W2. I spoke to the employer today and they said that they paid FICA on these wages and that was why they issued the W2 (?). They will not correct the W2.

Now what? I was thinking of answering the CP200 with an explanation that these were WC wages in the hopes that they would contact the employer.

Any thoughts???