Reproductive rights advocates in Texas have filed a new legal challenge to halt a near-total abortion ban that has been in effect for more than half a year.

Senate Bill 8 bars abortion once embryonic cardiac activity is detected – typically as early as six week of pregnancy, which is before most people are aware they are pregnant – and offers no exception for rape or incest. The lawsuit, filed on Tuesday, asks a federal court to rule the extreme law unconstitutional. It cites public threats and legal action from anti-abortion activists against Texas abortion funds, groups that have been instrumental in helping patients travel out of state for care, arguing that this conduct has chilled their first amendment rights.

“Plaintiffs urgently need this court to stop Texas’s brazen defiance of the rule of law, uphold the federal constitutional rights of pregnant Texans, and restore the ability of abortion funds and their donors, employees and volunteers to fully serve Texas abortion patients,” the federal court filing reads.

SB 8 is not directly enforced by government officials, but includes an unprecedented private enforcement provision that allows any individual – including anti-abortion vigilantes with no connection to the patient – to sue abortion providers or anyone who “aids or abet” care. Those who bring successful suits can win at least $10,000 in damages. The scheme – meant to evade judicial review – has thus far allowed the law to remain in effect, despite previous legal challenges.

The new lawsuit takes aim at a handful of anti-abortion activists in Texas as well as rightwing state lawmaker Briscoe Cain, who have all seized on the law’s novel enforcement provision by taking “steps” to sue or publicly threaten Texas abortion funds. In March, Cain sent cease-and-desist letters on his official letterhead to Texas abortion funds, and cited the “criminal abortion ban” – a Texas statute that pre-dates Roe v Wade, the 1973 supreme court decision that guarantees the right to abortion and that is presently under consideration by the US supreme court.

Cain also tweeted: “Prosecute Texas Abortion Funds”.

Lawyers say the hostile actions by Cain and activists are “chilling” the work of plaintiff Stigma Relief Fund, a non-profit that financially assists those who cannot afford abortion, by causing employees, donors and volunteers to end their relationships with the organization.

Wendy Davis, a former Texas senator who famously led an 11-hour filibuster against an anti-abortion bill in 2013 and later ran an unsuccessful bid for Texas governor, and abortion clinic director Marva Sadler, are also plaintiffs in the suit. They say they will no longer be donating to Texas abortion funds as the law is in effect due to the threats. The plaintiffs are represented by the Lawyering Project, who brought the suit in the US western district in Austin.

“We are asking the courts today to stop the unconstitutional harassment of abortion funds by confirming SB 8 cannot be used to silence donors with bogus threats,” said Davis in a statement.

“It is vital we show up for abortion funds and practical support organizations as they have shown up for pregnant Texans. If you want to fight back against abortion bans like Texas’s SB 8, donate to your local abortion fund and practical support organization today.”

Advocates hope the lawsuit will have more success than earlier challenges, after the US supreme court and the Texas supreme court ruled this year that the law could stand.

In March, two Texas abortion funds filed suit against two of the activists named in Tuesday’s suit in federal court outside of Texas, in order to evade the conservative fifth circuit court of appeals. Advocates hope the pressure of multiple lawsuits with differing strategies, defendants and venues will help legally erode SB 8.

Advocates say the law, in effect since 1 September due the US supreme court’s refusal to block the measure, has inflicted irreparable harm in a state that is home to 10% of the reproductive age population. Texans have been forced to travel hundreds or even thousands of miles for abortion access, overburdening clinics in surrounding states, according to the Guttmacher Institute.

Planned Parenthood clinics in Oklahoma alone – which is considering its own SB 8-style law – saw a nearly 2,500% increase in patients from Texas.

The ban has forced an average of nearly 1,400 Texans to travel out of state for abortion each month, nearly equal to the number that traveled every year between 2017 and 2019, according to research from the Texas Policy Evaluation Project. The influx of Texas patients to other states has in turn caused a ripple effect across the US reproductive health network.

Providers stress the law disproportionately affects the most vulnerable: low-income people, people of color, immigrants and young Texans, who are less likely to secure the resources necessary to venture out of state, including time off work, childcare and lodging. As a result, they are “suffering the physical and psychological impact” of unwanted pregnancy and giving birth “against their will or attempting to end their pregnancies without access to licensed healthcare providers”, the legal complaint says.

“Despite the remarkable efforts of abortion funds and practical support organizations, all too many Texans ultimately lack the resources or mobility to access abortion at great distances from home and thus face the devastating consequences of unwanted pregnancy,” said Rupali Sharma, senior counsel and director at the Lawyering Project. “Today, we are asking the court to end Texas’ defiance of the rule of law and uphold the fundamental rights of its residents.”

Several state legislatures have proposed copycat abortion bans modeled after Texas, with Idaho signing such a measure into law last month. Anti-abortion officials throughout the country are hoping such measures, unconstitutional under current precedent, will be allowed to stand, with the US supreme court expected to overturn or significantly chip away at the landmark Roe v Wade ruling in a forthcoming decision over a Mississippi 15-week abortion ban.