CBS News’ analysis of election data revealed that at least 16.800 mail ballots were returned in error across 14 of the 25 most populated counties. This is about 15% of all mail votes returned in these counties.

After months of opposition from Democrats and voting rights advocates, the rejections were recorded in the first major election after Texas Republicans passed a broad new election law. The bill was signed by Greg Abbott, Republican Governor of Texas, last September.

CBS News was informed by county election officials that the provision that caused the most problems for voters was the requirement that they present a driver’s licence number, personal identification number or the last four digits from their Social Security number when applying to return a mail ballot. The voter’s number must match the one on file.

According to Sam Taylor (assistant secretary of the state for communications at Texas secretary-of-state’s office), county election officials told the Texas Secretary of State’s Office that the “vast majority of” mail-in ballot rejections were due to the inability to provide correct identification information.

Harris County, which is home to Houston and third in population, had 6,888 rejected mail-in ballots out of 36,878 returned. This was due to compliance issues with the new voting law. This represents nearly 19% percent of all mail-in ballots. Only 31 ballots were rejected because they weren’t related to the new voting laws.

This year’s rejection rate for mail ballots was much higher than that of the previous midterm elections primaries. Officials claimed that only 135 of 48,473 mail ballots were rejected in the 2018 primaries. This is a rejection rate 0.3%.

Harris County’s elections office claims it has doubled its staff for voter outreach and contacting voters in the event of issues. Out of 7,750 ballots that were rejected, 849 people had corrected their ballots.

Isabel Longoria , Harris County Elections Administrator, announced earlier this week she would be stepping down on July 1, after being criticized by county leaders for her handling of March’s primary.

Harris County was not the only one affected by these problems. Nearly 22% of 18,000 returned mail ballots in Bexar County (which is also home to San Antonio) were rejected.

Collin County rejected approximately 14% of all mail in ballots that were returned to it. This is in the Dallas-Fort Worth metropolitan area. Bruce Sherbert of Collin County was the elections administrator and stated to CBS News that nearly all rejected ballots were due the new ID requirements in SB1.

Nearly 17% of all mail ballots were rejected in Denton County, which is also located in suburban Dallas-Fort Worth. According to the county elections department, 84% of those rejected were due to ID problems.

According to a spokesperson for Travis County’s clerk’s office, the majority of 896 rejected mail ballots in Austin’s Travis County — or about 8% of all votes — were not compliant with new ID requirements. 73% of the 521 mail ballots that were rejected in Williamson County, north of Austin, couldn’t count due to ID issues. Returning a ballot after the deadline was the next most common reason for rejection.

However, not all counties with large populations had such high rejection rates. Near Houston, Brazoria County rejected 3.6% percent of all returned mail ballots.

Texas already has stringent requirements regarding who can vote by mail. To be eligible for a mail ballot, voters must be at least 65, disabled, pregnant, or sick, and be out of county on Election Day.

In the weeks before the primary, there were signs that election officials were in trouble. A large number of mail ballot applications were denied for not complying with SB1. After the ballots were sent to voters, some counties rejected more than 30% of those returned ballots. However, they were able to reduce that number by aggressively contacting voters to correct their ballots.

Officials in Webb County, which is located near the Texas-Mexico border rejected 31 out of 734 returned mail votes, approximately 4%. Jose Luis Castillo, Webb County Elections Administrator, stated to CBS News that 112 ballots were originally flagged as invalid. This was mainly because they were not complete and did not meet all the requirements.

Castillo stated that voters have struggled but that it is more educational. Castillo stated that voters are used to the old system and not the new laws or requirements.

Texas secretary of state encouraged voters to update their information online in order to have all the identification that is associated with their registration. Both state and local officials encouraged voters to complete both ID numbers before they return a ballot.

Taylor is working with the Texas secretary-of-state’s office. He said that state and local officials would focus large amounts of voter education on new requirements for mail voters moving ahead.

Taylor stated that while in the past, we focused our voter education efforts only on ID requirements in person, this year we will also devote a substantial portion of our voter educational campaign to raising awareness about the new mail-in ballot ID requirement. “We feel confident that we have the data, research and information we need to use any lessons learned from the primary for an even stronger voter education campaign going into the November General Election.”