"We expect all companies we are invested in to have effective anti-corruption measures in place," fund chief Yngve Slyngstad said in a statement.
"Companies should have a whistleblowing mechanism that provides a separate and confidential escalation route when reporting through a line manager is not appropriate, or if the whistleblower wishes to remain anonymous," the fund said.
The Norwegian wealth fund, which has more than $1 trillion under management, regularly pushes companies in its portfolio to adopt more ethical practices, and often divests if they fail to do so.
Corruption costs the world around two percent of its wealth each year and hampers fair income distribution, the International Monetary Fund said in a 2016 report.
Kickbacks total between $1.5 and $2 trillion per year, the IMF said, the equivalent of the gross domestic product (GDP) of Italy or India.
The Norwegian sovereign fund, tasked with managing the country's oil wealth, is currently worth 8.128 trillion kroner ($1.028 trillion).
It is managed by the Norwegian central bank and follows ethical guidelines that prevent it from investing in companies that are guilty of serious human rights violations, make nuclear or other "particularly inhumane" weapons, produce coal or make tobacco products.