Employer didn't withhold federal taxes, now what?

We got my husband's w-2 forms and saw that they had withheld only 234$ for the year. For the income made, it should have been about 5 thousand. We checked the pay stubs and there were 8 months where they withheld 0$. The other deductions were all as the should be. They must of realized an error, because in November, there were some withholding for federal. I know we will have to pay a lot of taxes this year. I told them of the error and all they said is, is that they put a call in to their accountant. Are they liable for this mistake?