Updated 12:58 p.m. on Wednesday to include a new statement from Secretary of State Rolando Pablos.

AUSTIN — More than 2,000 Texans who registered to vote using an online tool provided by a California nonprofit could be in for a rude awakening on Election Day — they are not, in fact, officially registered.

In September, vote.org, which uses technology to increase voter turnout and bring more people into the political process, rolled out the tool to help Texans register for the November election. It was available in Dallas, Bexar, Cameron and Travis counties ahead of Tuesday's registration deadline.

Applications began rolling in, even from outside those four counties. But on Monday, the office of the secretary of state, the top elections administrator, told the nonprofit the applications submitted through it weren't valid because they didn't have original signatures.

In a statement on Wednesday, Secretary of State Rolando Pablos said: "We remind all eligible Texas voters that online voter registration is not available in the State of Texas. Any web site that misleadingly claims to assist voters in registering to vote online by simply submitting a digital signature is not authorized to do so. All Texas voters should be extremely cautious when handing over personal and sensitive information to any unknown third party."

He urged voters to check their registration status on the secretary of state's website, where they could also get more information on the elections.

On vote.org, applicants would answer questions that would auto-populate into a paper voter registration application. They would sign their name on a piece of paper, snap a photo of it and upload it to the online application.

The website would then fax and mail the application to elections administrators for processing. As long as the registrar received the mailed copy no later than the fourth day after the fax was received, the application should be valid, said Sarah Jackel, the nonprofit's general counsel.

Jackel said her group has used the tool in Alaska, Colorado, Kansas, South Carolina and Washington, D.C., without any problems. The group did not consult with the Secretary of State before launching in Texas, which does not have online voter registration and has some of the strictest voter identification laws in the nation.

Thirty-eight other states offer online voter registration or will soon, according to the Brennan Center for Justice at NYU School of Law.

Sam Taylor, a spokesman for the secretary of state's office, said registration applications require original signatures. The applications filed through the vote.org process contained only copies of signatures — in the appended photos — which made them invalid.

Affixing digital signatures to applications is illegal in Texas, Taylor said, and creates a high risk for fraud and abuse. The secretary of state's office notified vote.org that it objected to the online registration tool, and the nonprofit shut it down Tuesday.

"We disagree with their interpretation, but we didn't want any further voters in this situation," Jackel said. "The secretary of state basically created this situation where voters are potentially being disenfranchised when they were following part of Texas election code to register."

Taylor said the secretary of state is advising counties that received the applications to notify residents that they are incomplete. To finish registering, they will have to return applications with an original signature within 10 days of receiving the notice.

"Even if that 10th-day deadline falls after that Oct. 9 deadline, they would still have 10 days to sign an actionable form," Taylor said. "It's not going to affect whether or not these people are going to be registered."

But that still leaves thousands of Texas voters, including some in Dallas, who mistakenly think they have completed their voter registration. The Dallas County elections administrator did not respond to a request for comment.

Executives at vote.org said they are sending printed applications with stamped envelopes to people who registered using their tool so they can complete them for free. Counties will also have to send notices, at a cost to taxpayers.

"We have to," said Jacquelyn F. Callanen, elections administrator for Bexar County, which received more than 100 applications through the vote.org online tool.

There is also concern that some voters simply won't return the notices.

"For every hundred of these that we send out, I don’t know how many we’re going to get back," said Bruce Elfant, the Travis County voter registrar. "We're crafting a letter that is as simple as 'sign this and send it back.' We’re going to do everything we can to make these people whole. But we can't guarantee that they'll respond 100 percent."

Elfant, who estimates that Travis County received between 400 and 500 applications, said the snafu with vote.org's online tool was an "unfortunate misunderstanding."

He added: "If we had online voter registration, this problem would be solved. And a lot of others."