LAREDO, Texas—The Rio Grande Valley could be the next place border authorities target for a policy that arrests and criminally prosecutes all illegal immigrants caught crossing, a congressman said Friday.

U.S. Rep. Henry Cuellar, D-Texas, said he and other congressional leaders have already begun talking to authorities about the possibility of expanding the so-called “zero tolerance” policy downriver from Laredo.

Laredo will become the third U.S. border zone to begin enforcing the decades-old federal crime of illegal entry when it begins implementing the program next week. The program, which results in jail sentences of two weeks to six months for first-time convictions, began in Del Rio in 2005 and was expanded to western Arizona last year.

“This whole concept is very simple. All we’re doing is implementing the law,” Cuellar said at a news conference formally announcing the Laredo expansion.

Enforcement begins in Laredo next week, and Cuellar said he and others have already begun talking to authorities in the Rio Grande Valley about expanding soon, though he couldn’t say how long it might take to get the program started there.

U.S. Rep. John Culberson, R-Texas, said enforcement of the illegal entry law represents a sea change in the way that illegal immigration is handled in the United States.

Prior to zero-tolerance zones, Mexican migrants were most often voluntarily returned to Mexico, while those from other countries were given court dates they often skipped.

“We will not rest until zero tolerance is the policy from San Diego to Brownsville,” said Culberson.

Cuellar acknowledged, however, there will be an economic penalty to beefed-up enforcement without other changes that allow guest workers for jobs in agriculture and other industries where undocumented workers are most common.

“We need to educate a lot of people that the enforcement does affect the economy,” he said, adding that he hoped increased enforcement would encourage other immigration reforms.

Cuellar said it might also convince supporters of a border fence, which has been heavily opposed in border communities, that the barrier is no longer necessary.