Senate Bill 4 is set to go into effect September 1, but critics of the bill say it is still not clear what documents will be required to prove citizenship.

San Antonio criminal defense attorney Steven Gilmore said he thinks it's time to start gathering documents to prove citizenship under SB4.

"In Texas, it would probably be advisable to start carrying around social security cards, birth certificates, whatever you have," Gilmore said. "You don't know what's going to be sufficient to determine immigration status."

Gilmore said police officers will ask based on the color of a person's skin.

"Let's say you are undocumented and don't have an ID, how long can they detain you? Let's say you're a white person and you don't have your ID on you, are they going to detain you? Probably not." Gilmore said.

KENS 5 spoke with the Refugee and Immigrant Center for Education and Legal Services Agrees.

"If you are a person of color you're going to feel like you can get stopped and questioned by police," Policy Director Amy Fischer said. "That's not something that someone should have to feel, or be asked about when they are having a simple interaction with local law enforcement."

We reached out to San Antonio Police Chief William McManus to ask how officers will determine what documentation will prove citizenship. A public information officer responded 'the information has not been defined and will be part of training.'

Gilmore said it will be difficult for law enforcement to prove citizenship because many are here lawfully, but are not citizens.

"If you're here on a work visa, or u-visa, education visa, we don't know what's going to be sufficient," he said. "The law doesn't tell us what's going to work and what's not. It would be in your best interest to have as documentation as you possibly can to satisfy whatever requirements SB4 ends up having. Right now, we don't know."