Leinster duo Isa Nacewa and Jamison Gibson-Park have both been denied entry to South Africa ahead of their PRO14 fixture against the Southern Kings on Friday.
Nacewa, the Leinster captain, and scrum-half Gibson-Park ran into problems at O.R. Tambo airport after arriving in the country on Wednesday morning.
A new regulation was introduced by South African authorities in January this year, with the South African High Commission announcing the rule change last December.
"Effective on/after 16 January 2017, all diplomatic, official and ordinary passport holders of New Zealand will now require a visa to enter South Africa."
Friday's fixture is the first of two matches in the Republic for Leinster, who face the Cheetahs in Bloemfontein the following week.
"Leinster Rugby can confirm that two members of the touring squad to South Africa, Isa Nacewa and Jamison Gibson-Park, encountered visa issues this morning upon arrival in Johannesburg," read a club statement.
"As this process is still ongoing, Leinster Rugby will be making no further statement."
Leinster have won both of their opening league matches so far this season with a try bonus point.
The news is a blow for the PRO14 ahead of the league's first-ever fixture on South African soil on Friday evening at the Nelson Mandela Bay Stadium in Port Elizabeth.
Leinster have travelled with a squad of 28 to South Africa but are without a number of senior players, largely due to injury.
Among hose ruled out through injury include Dan Leavy (ankle), Rob Kearney (hamstring), Jamie Heaslip (lower back), Richardt Strauss (knee) and Garry Ringrose (shoulder).
Second-rows Devin Toner and Scott Fardy were not considered for selection with their wives due to give birth in the next few weeks.