[R-pkg-devel] Explicitly Calling a Method of a specific Class in a Function

Dear Developers,
I have currently one note in one of my packages I am unable to solve at my own:
?
checking dependencies in R code ... NOTE
Unexported object imported by a ':::' call: ?sp:::plot.SpatialPolygons?
  See the note in ?`:::` about the use of this operator.
?
The goal is to explicitly call the plot function of the 'SpatialPolygons-class' in the function ?plotWorldmap'.
In The CRAN checks the examples work. Manual calling 
of the function ?plotWorldmap' also works in an clean environment yielding the expected plot.
Thus, I assume the call
 sp:::plot.SpatialPolygons(world_country_polygons,col =cols,?)
is in principle correct. 

Could someone please help me?
What do I have to do or to change in order to disable this note?

Best Regards
M. Thrun