At a time when Republican opposition to President Barack Obama’s climate change initiatives is growing, the U.S. government announced Monday that it had deposited $500 million into the United Nations-backed Green Climate Fund (GCF). The payment marks the first tranche of the $3 billion the U.S. pledged for the GCF in 2014.

“This grant is the first step toward meeting the president’s commitment of $3bn to the GCF, and shows that the United States stands squarely behind our international climate commitments,” a State Department spokesman said Monday.

Developed nations have, so far, contributed over $10 billion to the GCF, which was established in 2010 with an aim to create a basket of funds to help developing nations mitigate the effects of anthropogenic climate change.

However, while the GCF has set an ambitious target of mobilizing $100 billion a year in climate finance from public and private sources by 2020, so far only a fraction of it has been raised.

“The focus has been too much on creating a political instrument than a financial instrument,” Yvo de Boer, who was the U.N. climate chief when the idea of establishing a fund was first raised in Copenhagen in 2009, told the Thomson Reuters Foundation.

Moreover, in the U.S., where Obama’s ambitious Clean Power Plan — which seeks to drastically cut pollution from power plants — has run into legal hurdles, the government’s $3 billion pledge for the GCF has also become a hot button issue. In November, for instance, several Republican members of Congress threatened to block federal funds for climate aid, before relenting during budget negotiations in December.

“We support international dialogue on global environmental problems. We do, however, have serious concerns about the impact any deal reached in Paris will have on the American economy and our international priorities,” a group of 37 senators wrote in letter to Obama, accusing the president of acting “unilaterally.”