Norway's $872-billion sovereign wealth fund, the world's largest, said it would press U.S. oil majors ExxonMobil and Chevron to do more to report on the risks of climate change.
The fund said on Tuesday it would vote in favor of shareholder proposals, opposed by both companies' boards, which would require them to report more fully about the risks and opportunities of a changing climate.
Royal Dutch Shell and BP adopted similar policies last year, following shareholder pressure, it said.
Exxon and Chevron both say they are already doing enough to report on climate risks.
"We want them to be open about their climate strategy and their dialogue with regulators," the fund's chief executive Yngve Slyngstad told reporters.
Firms should be clear about risks, both from the impacts of climate change such as floods and storms, as well as from government policies to curb carbon emissions, he said.
The fund, itself built from Norway's oil and gas wealth, was making similar demands of oil firms worldwide and would keep going even if the resolutions were defeated at Exxon's and Chevron's annual general meetings, both on May 25.
"We will then come back next year and the year after," he said. Norges Bank Investment Management (NBIM), which manages the fund, was the seventh-largest shareholder of both firms at the end of 2015, Thomson Reuters Eikon data shows.
Slyngstad said the fund, which owns about 1 percent of listed equities worldwide, had 4,000 meetings with major companies a year to discuss its investments.
He said many companies were planning to cut their greenhouse gas emissions by 40 percent in coming years to help achieve goals set at a 195-nation Paris summit on climate change in December that include phasing out emissions by 2100.
Companies "have to explain if they don't intend to reduce their emissions to that extent," he said.
The fund said last week that it may exclude another 40 companies for using coal in their operations after divesting from 52 since Norway's parliament last year told it to sell out of firms that get more than 30 percent of their turnover or activity from coal.
Slyngstad said it was hard to set firm rules, saying a power company generating 30 percent of its electricity from coal and 70 percent from wind might stay in the portfolio ahead of a firm using 30 percent coal and the rest fossil fuels.
"The fund is like a supertanker, It takes some time to turn it."
At the end of 2015, NBIM said it held a 0.78 percent stake in Exxon, valued at $2.54 billion, while its 0.85 percent holding in Chevron was worth $1.45 billion.