This is an issue that comes up regularly: whether legislators can be deposed in redistricting and voting-rights litigation when purpose-based challenges are made to these laws. From Scotus blog:

The Supreme Court on Monday afternoon denied a request from the leaders of the Arizona legislature to put on hold an order that would require them to be deposed about the legislature’s enactment of voting laws that make it more difficult to register to vote. In a brief unsigned order without any noted dissents, the justices turned down an emergency filing from Ben Toma, the speaker of the Arizona House of Representatives, and Warren Petersen, the president of the Arizona Senate.

The laws at the center of the dispute were enacted in 2022. They require would-be voters to provide proof of U.S. citizenship or face penalties, such as a ban on voting in most elections or an outright bar on voting by mail. The Biden administration and other plaintiffs, including the Democratic National Committee and the Arizona Democratic Party, went to federal court to challenge the laws, arguing that they violated (among other things) the 14th Amendment’s guarantee of equal protection and federal voting laws.