MADISON, Wis. -- A plan in the state budget might change the way that land for agriculture is taxed, and some farmers are crying foul.

Fourteen years ago, tax law changed to let more farmers keep farming, and many agree the law has worked. But some now some say because developers are benefiting too, the law should be amended, leaving some farmers paying a very high price.

"We just -- we'd be in trouble," said Randy Theis, a farmer at Theis Farms in Madison.

On the Theis family farm in Madison, Theis and his brother make a living on fields of corn and soybeans. The family farm has survived 70 years, partly due to a state law.

The "use-value assessment law" lets farmland gets taxed at a lower "agricultural" rate instead of at full market value.

But the state Senate has now changed that, leaving Theis and others fearful of the future -- and property tax hikes they can't afford.

"In all honesty, we could see a little increase. I could live with that, but not what could happen this way," Theis said.

Under the Senate amendment, Theis said he estimates property taxes on his 200 acres in Madison would go from more than $13,000 to nearly $300,000 on the family farm.

"We'd be forced to sell it right away, but, unfortunately, there are no buyers out there that are interested now. And us being in farming, we're not interested in selling anyway," Theis said.

But some groups said change is needed due to a supposed law loophole for developers.

Groups said the loophole lets developers buy up farmland and hold the land at cheap ag land tax rates, even though the land is clearly for -- and sometimes right next to -- other development.

The Wisconsin Alliance for Cities said that means ordinary homeowners are paying a higher tax rate than some developers.

"It gave them a huge tax break," said Ed Huck, of the Wisconsin Alliance of Cities. "Everyday people trying to work and pay their taxes should not be subsidizing somebody else's wealth."

But Theis said the law preserves farmland and lets developers he farms for react to the economy and build when conditions are right.

Still, the Senate disagrees. It has voted to no longer allow ag tax rates for ag land that is "platted or zone for residential commercial of industrial use."