Are you sure you mean the 1099? That's the category of informational returns filed to document a transaction. (Like you get 1099-Div for dividends, 1099-INT for interest).
If the PTO directly pays an independent contractor $600+ for services, it might have to provide a 1099-MISC. I believe the deadline to send these out is the end of January.
You might also be thinking about the 990/990EZ - which is the annual return a charitable organization files with the IRS that documents its revenue and expenses for the year. Most PTO's can file the 990EZ, the shorter version.
Filing is only required if you have more than $25,000 in gross proceeds (although many file it voluntarily with lesser amounts).
Form 990/990-EZ must be filed by the 15th day of the 5th month after the end of your organization's accounting period. So, for example, if your fiscal year ends in June - your filing deadline for the 990-EZ would be November 15.
Can anyone tell me when/if our PTO will have to give a 1099? We just received our 501c3 and I'm trying to make sure we get the routine items going right - rather than having to do them over.