The rising tide of legislation designed to bar judges from considering foreign and international laws could lead to constitutional challenges involving the separation of powers, the supremacy clause and civil rights violations against Muslims, according to a report released on Wednesday.

The New York University School of Law’s Brennan Center for Justice and the Center for American Progress concluded that the bans could lead to "decades of litigation" as courts struggle to interpret them against protections upheld in both the U.S. and state constitutions.

According to the report, 32 states have introduced bills within the past two years that would ban courts from interpreting foreign laws. The moves have been driven by an effort to prevent enforcement of Islamic religious codes, referred to as Sharia, based on the teachings of the Koran and interpretations by Muslim scholars.

None of the bans have specifically mentioned Sharia since the U.S. Court of Appeals for the Tenth Circuit in 2010 struck down a ban in Oklahoma that targeted that specific religious law. But the report cited constitutional issues in calling on legislators to reject the proposed bans and repeal laws that have been enacted in Arizona, Kansas, Louisiana, Oklahoma and Tennessee.

"Our report is basically about the unintended consequences and legal uncertainties that the second wave of foreign law bans would create," Amos Toh, a Brennan Center fellow who helped write the report. "There are a couple of constitutional problems with the bans."

The bans, many of which are broadly worded and use the terms interchangeably, would force judges to reject foreign laws or rulings—or entire legal systems—emanating from countries where individuals lack the rights they enjoy in the United States, according to the report.

That could lead to challenges over the U.S. Constitution’s separation of powers, since the bans would "interfere with the ability of state judges to look at international and foreign legal sources when they are trying to decide cases," Toh said.

The report found that the bans could interfere with ordinary cases that use foreign and international laws, such as those involving treaties or business disputes. Foreign and international law are two different things: Foreign law means the law of a foreign country, generally recognized by U.S. courts as long as it doesn’t conflict with public policy here; international law comprises "rules and principles governing the relations and dealings of nations with each other," such as treaties and executive agreements, the report says.

Since those international agreements are considered the law of the land, the bans could run afoul of the U.S. Constitution’s supremacy clause, Toh said.

"This could potentially be in violation of the supremacy clause because, ultimately, you can’t say that you want to ban state courts from enforcing treaties," he said. "Treaties are part of federal law."

Complications could arise in international business transactions drafted under foreign laws, or in the enforcement of court judgments in other countries. To that end, various business groups have spoken out against the bans, and legislators have inserted corporate exemptions.

But the uncertainties could dissuade businesses from conducting their affairs in those states, Toh said. Many of the exemptions, for example, don’t address whether they cover businesses that aren’t incorporated or individuals in a dispute with a corporation, he said. Furthermore, executives who come to those states for work might be dissuaded by the ban’s effects on their family disputes.

"The problem is, if we do want foreign investors and foreign business people to come here and invest and contribute business expertise, they also will ultimately want to bring their family here to settle down while they are contributing to the American economy," he said.

Marriages, divorces and premarital agreements often are based on religious laws in other countries, the report says. That is especially true in the Jewish faith, which has set up its own arbitration panels to resolve such disputes under its religious codes.

The bans spawn discrimination claims, particularly given the statements of some legislators specifically targeting Muslims, Toh said.

"Given that these bans are still very much motivated by that kind of venomous towards Muslims, there is definitely a question whether these bans would survive scrutiny under the First Amendment as well as equal protection clause," he said.

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