After Mr Skinner approached both Wal-Mart and Safeway spokespeople for both said they would investigate.
"As with all of our suppliers, we have a process underway to obtain documentation that [the company it buys its fish off is] complying with the laws regarding human trafficking and slavery, and that [they are] reviewing their supply chain to insure compliance," Brian Dowling, Safeway's vice president of public affairs, said.
"We have not yet received certification from [the company]. However, we are following up with them immediately and asking that they provide us with certification."
In July last year a ministerial inquiry into foreign-owned fishing vessels in New Zealand's waters was launched - the findings of which would be released on Friday.
Primary Industries Minister David Carter said the Government was fully aware of concerns raised about the use of foreign charter vessels in New Zealand waters.
"Which is why a joint ministerial inquiry into the operation of FCVs was launched last year. The inquiry panel is due to report this week and until the Government has considered the report and its recommendations, ministers will not be making any further comment."
The Government respected that the American retailers might have raised concerns about the operation of FCVs in New Zealand waters, he said.
"New Zealand works hard to uphold its international reputation as a world-leading fisheries manager, which is why the Government initiated the ministerial inquiry into the operation of FCVs when issues were raised last year."
New Zealand Seafood Industry Council chief executive Peter Bodeker said it was critical the council heard the outcome of the inquiry before determining what long-term actions might be needed.
"The New Zealand seafood industry does not condone the slavery and inhumane treatment that is being alleged, and in fact called for a Government inquiry into foreign-owned fishing vessels in July last year."
It was too early to determine any, or what, impact American retailers' investigations might have on New Zealand's fishing industry, he said.
The ministerial inquiry's main objectives were to ensure foreign vessels supported the Government's objectives of protecting New Zealand's international reputation and trade access, maximised the economic return to New Zealand, and ensured acceptable and equitable New Zealand labour standards.