Texas Gov. Greg Abbott issued a proclamation Thursday limiting the amount of drop-off locations for mail-in ballots to one site per county.

The move significantly affects the Democratic stronghold of Harris County, which is the state’s largest county by population — one of the most populous in the country — and covers a massive area. It must now reduce its 11 drop-off locations down to one starting on Friday. Travis County, which includes the reliably Democratic city of Austin, must limit its four drop-off locations to one.

Other large counties — like Tarrant, Dallas and El Paso County — only had one drop-off location already in place.

The Republican governor said in a statement the order was made to enhance ballot security. It also allows poll watchers to observe the in-person delivery of mail-in ballots by voters, but critics say it could severely limit access for many voters.