This op-ed originally appeared in the The San Antonio Express-News.

The first skirmish in the legal battle against the most anti-law enforcement and anti-immigrant law in the country begins today.

My colleagues and I at the ACLU will argue before the federal district court in San Antonio that Texas’ patently unconstitutional Senate Bill 4 prevents our clients — the city of El Cenizo and its mayor, Raul Reyes, and Maverick County and its elected officials — from protecting their communities effectively, and infringes on the rights and liberties of our clients at Texas LULAC.

We are seeking to block SB 4 from taking effect Sept. 1 as scheduled.

The First Amendment is unyielding in its protection of the expression of opinions, yet SB 4 ignores that protection and punishes any local official who refuses to “endorse” it.

The due process clause of the Fifth and 14th amendments requires that a law be explicit in what it allows and what it prohibits. But SB 4 is so vaguely written and so broad in scope that law enforcement agencies are left to guess, and failing to guess correctly can lead to removal from office, jail time and fines of up to $25,500 per day.

The Fourth Amendment prohibits detaining anyone without probable cause or a warrant signed by a judge. But the ICE detainer requests — which SB 4 requires local governments to honor — fail to meet those standards and would lead to unconstitutional detentions.

But SB 4’s constitutional failings are still not as insidious as the devastating effect this misguided law will have on Texas communities. Both the senator who authored the bill and Gov. Greg Abbott who signed it expect us to believe that SB 4 is necessary because Texas law enforcement leaders cannot be trusted to uphold the law. But their disingenuous justification ignores the accounts of community members, the pleas from law enforcement chiefs, and all available evidence, all of which demonstrate that SB 4 will make Texas less safe, not more.

The sheriffs and police chiefs of Texas are not pro-crime, but they are in favor of effectively protecting the communities where they live and serve. Indeed, so many of them oppose SB 4 precisely because it will compromise their ability to defend their residents’ constitutional rights and will erode the trust they’ve built with their communities. With SB 4 enforced as written, patients will fear traveling to clinicsChildren will fear traveling to schoolVictims of crime will fear coming forwardWitnesses will hold their tongues.

SB 4 will also subject countless Texans — whether citizens or not — to racial and ethnic profiling because of the clothes they’re wearing, the language they’re speaking, or simply because they “look like they’re not from around here.” In fact, it’s already happening; recently state Rep. Matt Rinaldi felt emboldened enough to alert ICE to a group of peaceful protesters at the Capitol, based on nothing other than his perception that they were “illegal.”

Racial discrimination against Latinos will manifest in more than subtle forms, resulting in roundups, arrests, unlawful detentions and mistreatment.

And finally, SB 4 will compel every peace officer in the state to serve the will of the federal government. And this from a governor who has sued the federal government 48 times for “overreach.”

For these reasons and more, my ACLU team is headed to court. This is not the first time we’ve defended immigrants’ rights, and for that matter, not the first time we’ve defended immigrants’ rights in San Antonio. In fact, the ACLU of Texas cut its teeth there defending the constitutional rights of Mexican-American and immigrant pecan shellers back in 1938.

Our latest legal battle is every bit as important as our first, but SB 4 is not just another anti-immigrant law poorly masquerading as a commitment to public safety. As a person of color and the son of Mexican immigrants, I’m keen to the bitter sting of discrimination and recognize SB 4 as a betrayal not only of our indispensable immigrant communities in Texas but of our commitment to equality as a nation.