Some schools are strict with their deadlines, while others are more lenient if you ask them beforehand. Therefore, I would suggest that you send an email asap explaining your situation. However, keep in mind that if you haven't already done so, it might take them a couple of days to reply. Also, while it might take some courage to 'pressure' recommenders, this is about your future and won't hurt to try to get them to submit the LoRs by the deadline. Good luck!
SIPA has two deadlines. January 6th is if you want to be considered for fellowships, February is if you don't want to be considered for fellowships.