Kansas Secretary of State Kris Kobach (R), the official leading President Donald Trump s voter fraud probe, apparently sought to amend federal voting law to make it possible to require proof of citizenship during the voter registration process, according to an email made public Friday as part of an ongoing lawsuit with the American Civil Liberties Union.

The email offers the firmest evidence yet that Kobach was interested in amending the 1993 National Voter Registration Act , as has been speculated. The NVRA a law championed by voting advocates requires motor vehicle, public assistance and some other state agencies to provide voter registration opportunities, and outlines the procedure by which voters can be removed from the rolls.

On Nov. 9, the day after Trump was elected president, Gene Hamilton, a member of Trumps presidential transition team, emailed Kobach with what he called Day One immigration policy action items. Kobach responded by saying he had already begun work on proposed legislation targeting the NVRA.

We will... be putting together information on legislation drafts for submission to Congress early in the administration, Kobach told Hamilton in an email. I have some already started regarding amendments to the NVRA to make clear that proof of citizenship requirements are permitted (based on my ongoing litigation with the ACLU over this).

In a July 7 email to the ACLU also filed as part of court documents, Garrett Roe, Kobachs attorney, noted the November email only referred to the possibility of a draft NVRA amendment and that the draft was never sent.

The email lends fuel to accusations by critics that Kobach and the Trump administration could be using the Presidential Advisory Commission on Election Integrity , of which Kobach is the vice chair and de facto leader, as a pretext for changing the NVRA with the aim of making it more difficult for Americans to vote.

Kobach did not immediately respond to a request for comment for this article.