The US Supreme Court on Monday failed to resolve a major case involving the Obamacare law's mandatory birth control coverage, telling lower courts to reconsider the matter after tossing out their rulings favouring President Barack Obama.

The court, which is deadlocked following the death of conservative Justice Antonin Scalia, did not rule on the merits of the legal challenge by Christian employers who objected to the 2010 healthcare law's requirement that they provide female workers with medical insurance paying for contraceptives.

It threw out seven rulings by federal appeals courts around the country that had backed the Obama administration.

The justices handed at least a short-term victory to the religious employers, primarily Roman Catholic organisations.

The decision suggested a possible compromise for the lower courts that would allow women to get contraception coverage without violating the religious rights of employers, by having the government arrange coverage directly with health insurers rather than requiring employers to sign off on it.

Among the employers challenging the contraception mandate were the Roman Catholic archdioceses of Washington and Pittsburgh, the Little Sisters of the Poor order of nuns, and Christian colleges.

Another organisation, Priests for Life, attacked the Supreme Court's move. Its national director Fr Frank Pavone said: "One of the key issues at stake in the 2016 elections is religious freedom, and the persistent effort of the Obama administration to force priests and other believers to violate their faith by providing abortion-inducing drugs and contraceptives in their health care insurance."

He added that the action by the Court "does not make the issue go away, nor will it make voters forget the stark political differences between those who respect religious freedom and those who do not."

Gretchen Borchelt of the National Women's Law Center said: "We are disappointed that the court did not resolve once and for all whether the religious beliefs of religiously affiliated nonprofit employers can block women's seamless access to birth control."

Additional reporting by Reuters.