I would use the EIN. Both would work, but I would avoid giving out my Social Security number to anybody that does not need it.
If it is filed by August 1st, the penalty is $100 (see first link). See the second link for the address to mail it.
<a rel="nofollow" target="_blank" href="
https://www.irs.gov/pub/irs-prior/i1099gi--2016.pdf#page=18">https://www.irs.gov/pub/irs-prior/i1099...>
<a rel="nofollow" target="_blank" href="
https://www.irs.gov/pub/irs-prior/i1099gi--2016.pdf#page=7">https://www.irs.gov/pub/irs-prior/i1099g...>
