A Catholic charity is under fire for allegedly restricting access to contraceptive and abortion services for undocumented immigrants, according to a lawsuit by the American Civil Liberties Union (ACLU).

The nonpartisan organisation is seeking records of the United States Conference of Catholic Bishops (USCCB) to see what type of reproductive health services the agency has been providing or withholding from unaccompanied minors.

The USCCB has a government contract to care for the tens of thousands of undocumented immigrant minors who cross the Mexican border without guardians each year. In 2014, there were nearly 60,000 of these youth, and almost a third were female. According to the ACLU, up to 80 per cent of the girls were victims of sexual assault.

"We have heard reports that Catholic bishops are prohibiting Catholic charities from allowing teens in their care to access critical services like contraception and abortion— even if the teenager has been raped on her journey to the United States or in a detention facility," ACLU staff attorney Brigitte Amiri reported.

The USCCB objects to abortions, in accordance with Catholic beliefs, and maintains that it is in their right to refuse to provide such services.

"For decades, we have provided exemplary services to this vulnerable population without facilitating abortions, and despite ACLU's extreme assertions to the contrary, the law not only permits our doing so, but protects it," Kevin Appleby, Director of the USCCB's Office of Migration Policy and Public Affairs, told Fox News.

Appleby said that girls requesting abortions are reported to the federal government, if the government has legal custody of them. The organisation's policy for other minors or for those requesting contraception is unclear.

The ACLU indicated that they will consider further legal action depending on what they learn from the requested USCCB documents. The Catholic organisation has received $73 million from the government for the care of the undocumented minors.