Illinois voting rights advocates have launched an effort aimed at overriding Gov. Bruce Rauner's controversial veto of the automatic voter registration bill.

The governor vetoed the bill Friday, which was the deadline for him to act on the legislation.

Since then, the good government group Common Cause Illinois reports that over 6,000 of its members have contacted their respective state lawmakers as of Tuesday morning, pressing them to support an override vote in the fall veto session.

The bipartisan legislation passed the Illinois General Assembly with votes of 86-30 in the House and 50-7 in the Senate. Proponents are cautiously optimistic that there will be enough support for a veto override.

"We're optimistic, but we're not taking anything for granted," said Trevor Gervais, lead organizer with Common Cause Illinois, which has over 20,000 members. "Our members will be out in the districts knocking on doors, talking to voters, making phone calls and making sure we can hold these (lawmakers) accountable to their original vote."

Common Cause Illinois is with the Just Democracy Coalition, a group of 65 organizations that advocated for the automatic voter registration bill.

"We're beyond disappointed [by the governor's veto], but we're turning that disappointment into action, and we'll be very active over the coming months," Gervais said.

Five U.S. states have already adopted automatic voter registration: California, Connecticut, Oregon, Vermont and West Virginia.

The Illinois legislation would give several state agencies the authority to automatically register eligible voters starting in January 2018, unless they opt out of the program. Additionally, registered Illinois voters would be able to update their voter information when they interact with participating state agencies.

For his part, Rauner has described himself as a "strong advocate for modernizing our election system and easing voter access."

He vetoed the automatic voter registration bill over concerns that it clashes with federal election law and could lead to voter fraud, specifically among non-citizens. The governor also raised questions about the reliability of state agency information, the measure's implementation timeline and resources needed for the effort.

In his veto message, Rauner recommended several changes to the legislation and said he is "hopeful that these concerns can be addressed and we can together enact a bill that achieves our shared goals."

Proponents have pushed back on Rauner's reasons for vetoing the legislation, accusing him of playing "partisan politics with an issue so important as voting rights."

Gervais claimed that the administration came to the coalition with its concerns about the bill on the Monday before the governor's Friday deadline.

"We had no problem with about 90 percent of those changes," Gervais said. "The one that they weren't going to move on was the fact that they wanted (the legislation's start date) moved to 2019."

Rauner plans to seek re-election in 2018.

The bill, Gervais said, was drafted with feedback from all stakeholders, and "every single person that we talked to said 2018 is more than doable, more than reasonable."

"The idea that the governor comes in at the last minute and says because of implementation reasons it has to be after his election, frankly, it's fairly clear the motivation behind that," Gervais said.

State Sen. Andy Manar (D-Bunker Hill) and state Rep. Robyn Gabel (D-Evanston) spearheaded the automatic voter registration bill in their respective chambers.

"I am very disappointed by the Governor's veto, and I am committed to continuing to fight to ensure every citizen in this state is enfranchised," Gabel said in a Facebook post Monday.

"I am determined to ensure we have legislation in November - either a veto override or legislation for which we can all vote," she added.