Documents required for B1 visa for Indian re State Government employees

[gujarathi_p]

Hi,

My sister is in US holding Green card. My sister would like to invite my parents for US visit on B1 visa and they'll sponser for the trip. I have required information about required documents from sponser. But, I need help about required documents from my parents.

My parents are Indian state government employees and are still in service. I have following questions:

1) What are the documents required from my parents?
2) Do my parents need to provide No Objection Letter from the govt. authorities?
2) Do they need to provide proof / letter about sactioned leave from higher authorities with the period?

Thanks,
Praveen