Activists in Arizona are expressing concern over how the U.S. Supreme Court may rule after reviewing the constitutionality of Prop 200, a state law that demands that voters prove that they are U.S. citizens before registering to vote or casting a ballot.

“Although this law was approved in Arizona in 2004, we’re seeing a phenomenon throughout the country where rules have been implemented to make the process of voting more difficult, using fraud as an excuse,” Alessandra Soler, the ACLE chief in Arizona, told Efe.

The nine magistrates of the Supreme Court earlier had rejected the request by the Arizona government to block a federal appellate panel ruling against Prop 200.

While Proposition 200 was approved in a referendum in 2004, it is anticipated that the definitive ruling by the high court will come after the Nov. 6 elections.

The 9th Circuit Court of Appeals said in its ruling that federal law takes precedence over the Arizona state law.

Soler said that so far nobody has been charged in Arizona with voter fraud.