The new law was signed by Republican Governor Mike Parson in May and is set to go into effect on August 28.

The 31-page complaint filed in the US District Court for the Western District of Missouri contends that the legislation is unconstitutional.

It asks for an injunction to stop the law from being enacted next month until the complaint is resolved.

“Without this relief, the bans will have a devastating effect on patients seeking access to abortion in the state,” lawyers wrote in the complaint.

The law is one of the most restrictive in the nation and activists contend it effectively forbids most abortions since many women do not know they are pregnant yet at eight weeks.

In a perennially divisive moral and political fight, similar laws have been proposed in more than a dozen other US states as Republican-controlled legislatures flex their muscles.

Efforts to roll back Roe v. Wade, the US Supreme Court decision legalising abortion in 1973, have been emboldened by two appointments by president Donald Trump giving conservatives a solid majority on the court.

Neither representatives for the Missouri governor’s office, nor lawyers for the ACLU and Planned Parenthood, were immediately available for comment early Wednesday.

Parson said in may that the new law would make Missouri “one of the strongest pro-life states in the country.”

The legislation allows for an abortion after the eighth week only in the case of medical emergencies, and provides no exceptions for victims or rape or incest.

Plaintiffs in the Missouri complaint said the law conflicts with more than four decades of binding precedent, would prohibit “the vast majority of pre-viability abortions”, and denied patients healthcare they were entitled to.

Planned Parenthood is engaged in separate litigation with the state to keep a St. Louis clinic open.

If Missouri officials succeed in closing the clinic, it would become the only US state without a legal abortion facility.