State law passed last year gave Nebraska Gov. Dave Heinemen, a Republican, authority to hand power of eminent domain over landowners to TransCanada.
The federal government needs to sign off on Keystone XL, which would cross the U.S.-Canadian border. State laws govern route decisions, however.
Randy Thompson, a Nebraska farmer taking part in a case challenging the law, said the measure is unconstitutional.
"By all appearances, that bill was written by TransCanada," he was quoted as saying Sunday by The Washington Post. "I think at some point in time, ordinary citizens can't tolerate that kind of behavior."
Concerns over a previous pipeline route through a Nebraska drinking-water aquifer prompted TransCanada to revise the state route. TransCanada spokesman Shawn Howard told the newspaper planning would continue despite the latest legal challenge.
A Nebraska judge in Lancaster County set a Sept. 27 trial date for arguments.
President Obama said he'd weigh the project against its environmental footprint. A section of the pipeline from Oklahoma to southern U.S. refineries is under construction.