A group of doctors announced Wednesday that they will file suit against the State of Texas, six months before a new law is expected to shutter 18 of Texas’ 25 existing legal abortion facilities. The providers are represented by the Center for Reproductive Rights (CRR), which also represented some of the same medical professionals in a lawsuit against the state filed last fall.

In a statement, CRR President Nancy Northrup said that her organization “filed this lawsuit to stop the second-largest state in the nation from plunging millions of women back into the darkness and grave danger of illegal abortion that Roe v. Wade was supposed to end.”

The lawsuit challenges two provisions of HB 2, the omnibus anti-abortion law passed last summer after a special legislative session saw thousands of Texans descend on their state capitol in support of reproductive rights following state Sen. Wendy Davis’ 13-hour filibuster of the bill.

The plaintiffs, which include providers from El Paso, Central Texas, Dallas, and the Rio Grande Valley, are asking for a court order that would prevent abortion providers from having to renovate—or build anew—facilities to mirror hospital-style ambulatory surgical centers (ASC), construction that can often cost millions of dollars. Though the conservative sponsors of HB 2 claimed that its intent was to improve patient safety, when the law was passed last summer, Texas Lt. Gov. David Dewhurst, a Republican, tweeted that it was intended to shutter as many legal abortion providers as possible.

Only six existing ambulatory surgical centers in Texas provide abortions, with a seventh tentatively expected to open in San Antonio this fall. If HB 2’s ASC requirements go into effect, about three-quarters of Texas abortion providers would be forced to close, and none would remain open west or south of San Antonio, or east of Houston.

Secondly, two abortion providers in far south and far west Texas are asking the court to block the provision of HB 2 that requires them to have hospital admitting privileges if they perform legal abortions. That provision ended access to legal abortion in Texas’ Rio Grande Valley in November 2013.

In January, the Fifth Circuit Court of Appeals heard arguments in an earlier lawsuit brought against the state by some of the same plaintiffs, and last week a three-judge panel issued an opinion in favor of the State of Texas, ruling that the provisions of HB 2 that heavily restrict the prescription of medication abortions and which require abortion providers to obtain hospital admitting privileges are constitutional, and do not impose an “undue burden” on Texans seeking legal abortion procedures.

Researchers at the University of Texas’ Texas Policy Evaluation Project have estimated that more than 22,000 Texans would be unable to access legal abortion as a result of those two provisions. Critics of the law say the impact is expected to be much greater if the state is left with only a handful of legal abortion providers, located only in major metropolitan areas.