The most radical abortion law in the US has gone into effect, despite legal efforts to block it.

A near-total abortion ban in Texas empowers any private citizen to sue an abortion provider who violates the law, opening the floodgates to harassing and frivolous lawsuits from anti-abortion vigilantes that could eventually shutter most clinics in the state.

“Abortion access will be thrown into absolute chaos,” says Amanda Williams, executive director of the abortion support group the Lilith Fund, a plaintiff in the suit that challenged the law. “Unfortunately, many people who need access the most will slip through the cracks, as we have seen over the years with the relentless attacks here in our state.

“It is unbelievable that Texas politicians have gotten away with this devastating and cruel law that will harm so many.”

Senate Bill 8, ushered through the Republican-dominated Texas legislature and signed into law by the Republican governor, Greg Abbott, in May, bars abortion once embryonic cardiac activity is detected, which is around six weeks, and offers no exceptions for rape or incest. Texas is the first state to ban abortion this early in pregnancy since Roe v Wade, and last-minute efforts to halt it through an appeal to the US supreme court by Tuesday did not succeed.