Supporters say it's the world's most ambitious green investment rulebook.

Critics say it's just "greenwashing".

So what is the EU's sustainable finance taxonomy?

The EU taxonomy is a system to classify which parts of the economy can be marketed as sustainable.

It includes a list of activities, plus criteria that each must meet to earn a green label.

Rules for most sectors came into effect in February.

But rules for gas and nuclear energy have been delayed amid disputes over whether the fuels help fight climate change.

The European Commission proposed investments in some gas and nuclear power plants would be labelled as sustainable.

EU financial services chief Mairead McGuinness:

"So today, we're setting out how gas and nuclear could make a contribution in the difficult transition to climate neutrality. We're putting in place strict conditions for their inclusion in the taxonomy. They are subject to clear limits and phase-out periods."

The decision is opposed by campaigners, the EU's expert advisers, some investors and countries.

Some European lawmakers say they will try to block it.

The EU's goal to eliminate its net emissions by 2050 will require huge investments, much of it private funding.

The taxonomy does not ban investment in activities not labelled "green".

But it limits which ones can be called climate-friendly.

That’s meant to stop greenwashing, when firms exaggerate their eco-credentials.

Providers of financial products must disclose which investments comply.

Large firms must also say what share of their turnover and capital expenditure complies.

Polluting companies can get credit for making green investments, such as an oil firm investing in wind power.

So what makes a "green" investment?

First, those that contribute to green goals, like wind farms.

Second, those that enable other green activities -- for example, facilities that can store electricity.

Third, transitional activities that cannot yet be made sustainable, but which have emissions below industry average

Gas and nuclear power plants are classed as transitional.

EU policymakers had hoped to finish the rules in 2020.

In the end they published a first set of rules in April 2021 for sectors including transport and buildings.

..and delayed gas and nuclear criteria until now.

Under the final rules now published, gas plants would be labelled green, if they meet criteria including emissions limits.

Nuclear plants must receive construction permits before 2045 to get a green label, and be located in a country with a plan to safely dispose of radioactive waste.

[McGuinness] "I think that's fair to say that overall the feedback were received showed that positions are widely divided."

"And (Let me) be very clear, it's the same with gas. There is no "Get out of Jail" (Monopoly board game card) here for nuclear or gas. We are saying very clearly that these are instruments in transition to allow us get to where we need to be, which is more and more renewables."

Austria has threatened legal action over nuclear's green label.

While opponents cite concerns over waste disposal, pro-nuclear states like France say the CO2-free energy is crucial to climate targets.

Gas is divisive too. Denmark, Ireland and others say calling it green would undermine EU leadership on climate change.

The taxonomy is not finished.

To be deemed green, an activity must aid one of six environmental aims and not harm the other five.

The rules published so far cover two aims:

fighting climate change, and adapting to its impacts.

Criteria for the others will follow in 2022.

The EU has delayed a contentious decision on whether to label agriculture, potentially including intensive farming, as climate-friendly.