A private border wall construction project lauded by Trumpers nationwide is actually partially on Mexican soil, Mexican government engineers alleged in photos their American counterparts shared with the builders this month.

Tempting an international incident, the border wall group isn’t budging.

Instead, they’ve moved to attack mode, with their founder calling the binational body that governs the border “50% OWNED by MEXICO” and “UN like” — fighting words, among private border wall fundraisers.

Brian Kolfage, whose group “We Build The Wall” has raised a whopping $25 million for border wall construction on GoFundMe, estimated that the “boulders” from his wall project currently on the Mexican side of the border weighed around two hundred pounds each.

His contractor has refused to move them, he said.

“Our construction guy said he’s not touching them, that he’s not going to move the rocks at all,” Kolfage told TPM. “It’s such B.S.”

So will We Build The Wall remain in Mexico?

“I assume so,” he said. (The contractor, Fisher Industries, didn’t respond to a request for comment.)

That’s a problem for the Mexican government, and for the International Boundary and Water Commission (IBWC), established in 1889 with one commissioner from each country. (The current U.S. commissioner is a Trump appointee.)

“Contractor must remove all fill that encroached into Mexico,” the commission told We Build The Wall earlier this month, as first reported by the Kansas City Star.

What if the group won’t budge?

Our instructions “speak for themselves,” IBWC Foreign Affairs Officer Sally Spener told TPM.

Can a binational commission force an American contractor onto Mexican soil to remove tons of boulders?

“That is a legal question that I cannot respond to at this time,” said Spener.

“There’s nothing they can do,” Kolfage told TPM.

Nothing?

Kolfage conceded that “the Mexican government could bring it up to President Trump and run it up the political chain and try to get it handled.”

The IBWC regularly handles issues of binational importance, most notably water that flows across the border, and the 130-year-old body could hold firm in its beef with the GoFundMe wall builders, even if the group counts former White House adviser Steve Bannon as an adviser and former Kansas Secretary of State Kris Kobach as general counsel.

It’s not the first time We Build The Wall has had a run-in with the commission.

Take the gate they built at the end of their wall that extends beyond the private property on which the wall sits. When closed, it blocks the government from accessing a levee road next to the Rio Grande. IBWC maintains that the gate was built “without a permit,” and initially locked it open.

Kolfage, characteristically, blasted the gate dispute across social media and urged his hundreds of thousands of donors and followers to urge the commission to do the right thing. Now, the gate is locked closed at night and open during the day as negotiations continue.

Kolfage claimed the landowner in Mexico next to the private wall is fine with the new boulders on his property: He “doesn’t have a problem with the rocks being there at all,” Kolfage said.

Spener, the IBWC foreign affairs officer, was unimpressed.

“The concern about the encroachments was brought to our attention by the Mexican government,” she wrote, “which is the entity we deal with.”