SpaceX has been working with NASA to demonstrate its Dragon capsule is ready to begin regular cargo resupply runs to the ISS.
NASA said last week the launch from Cape Canaveral could occur by early April, but SpaceX's latest tentative date reserved with the Eastern Range launch facility indicates it won't happen before April 20, Florida Today reported Friday.
And other traffic to and from the station in late April could delay the launch even further, the newspaper said.
SpaceX has had to delay its intended launch date several times.
"The primary driver for the schedule continues to be the need to conduct extensive software testing," a SpaceX spokeswoman said in a statement.