Multiple Texas counties on Tuesday will declare that the migrant crisis at the southern border is an "invasion," Fox News has learned, a move that could lead to similar declarations across the state.

Kinney County Judge Tully Shahan is expected to announce the move at a news conference Tuesday afternoon, along with a number of other officials from other counties who will join him.

Kinney County Attorney Brent Smith told Fox News Digital that he believes approximately 12 to15 counties could end up having declared an invasion by the end of the month.

With migrant numbers hitting historic levels, and with more than 239,000 migrant encounters in May alone, there has been considerable talk in conservative circles about the merits of declaring the crisis an "invasion" -- which could open up a number of potential legal avenues for states.

ARIZONA AG BRNOVICH ISSUES LEGAL OPINION DECLARING BORDER CRISIS ‘INVASION’ UNDER CONSTITUTION

Border Patrol agents behind fence

Both federal and state law enforcement agencies are sending reinforcements to the southern border as CBP border encounters nearly hit 240,000 in May.  (Eddie Seal/Bloomberg via Getty Images)

Former Office of Management and Budget (OMB) Director Russ Vought and former acting deputy DHS Secretary Ken Cuccinelli, both now at the Center for Renewing America have urged governors to make the declarations and use war powers to order Arizona’s police or National Guard to remove illegal immigrants to Mexico themselves.

They have pointed to language in Article I of the Constitution, which allows for States to "engage in War" when it has been "actually invaded, or in such imminent Danger as will not admit of delay" without the approval of Congress. They also note Article IV says the U.S. "shall protect each [state] against invasion."

The idea scored a major win in February, when Arizona Attorney General Mark Brnovich issued a legal opinion declaring the crisis an invasion, arguing that the definition of "invasion" contained under the U.S. Constitution is not limited to hostile foreign states, and can include "hostile non-state actors." 

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"The violence and lawlessness at the border caused by transnational cartels and gangs satisfies the definition of an ‘invasion’ under the U.S. Constitution, and Arizona therefore has the power to defend itself from this invasion under the Governor’s authority as Commander-in-Chief," Brnovich wrote. "An actual invasion permits the State to engage in defensive actions within its own territory at or near its border." 

Cuccinelli told Fox News Digital that the move by the Texas counties was significant and should now put more pressure on Texas Gov. Greg Abbott to make the declaration himself.

"The key here is you've got the first legal ruling that the southern border situation is an invasion," he said. " One, that's obviously very significant, and two it's going to -- as it should -- put enormous pressure on Governor Abbott to adopt that position themselves and to respond accordingly."

Kinney County itself is a rural county and officials there have estimated that they have seen thousands of illegal immigrants crossing through the county in recent weeks.

Migrants released into United States

Jan. 23, 2022: Fox News footage shows migrants being released into the US. (Fox News)

Kinney County Attorney Smith told Fox News Digital that he saw the move as standing with Gov. Abbott in taking unprecedented action against what he believes is a failure by the Biden administration to take appropriate action at the federal level.

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"Last week Governor Abbott was in Eagle Pass and he said something to the effect of unprecedented times calls for unprecedented action or measures. And the counties that have declared an invasion agree with Governor Abbott that these are unprecedented times where local and state governments have to work together and take unprecedented action," he said. 

"And the only reason we have to do this is because President Biden has failed to secure the border at all. So we're standing with the governor and we're declaring an invasion in the hope that he will stand with us in doing so," he said.

The move comes after the state was dealt a defeat at the Supreme Court last week when the high court ruled against Texas, finding that the Biden administration could unravel the Trump-era Migrant Protection Protocols (MPP)