UNITED NATIONS — The Trump administration informed Congress on Monday that it had terminated United States funding for the United Nations Population Fund, the world’s leading provider of family planning services, including contraception, to women in at least 155 countries.

The United States is one of the top donor nations to the United Nations, and the denial of funding was one of President Trump’s biggest moves yet to reduce financing for family planning.

While the administration had signaled back in January that was adopting a tougher stance toward family planning services that provide abortion counseling, the move was nonetheless a stunning piece of news to advocates for women’s and children’s health, particularly in the developing world.

In a letter to the Senate Foreign Relations Committee, the State Department’s Bureau of Legislative Affairs said it had determined that the Population Fund “supports or participates in the management of a program of coercive abortion or involuntary sterilization,” a reference to the Kemp-Kasten Amendment, a 1980s-era law enacted in response to evidence of forced abortions and involuntary sterilization in China.