Colorado's Democratic U.S. Sen Mark Udall says he'll introduce a measure next week to permanently block any Army move to expand Fort Carson's Pinon Canyon Maneuver Site.

The training area has been at the center of controversy for nearly a decade amid Army ambitions, since renounced, to add 100,000 acres to the 235,000-acre site east of Trinidad. Ranchers in the sparsely-populated region of Las Animas County oppose the Army plans and formed a coalition that included politicians, peace activists and environmentalists.

Since 2008, the Army has contended that it doesn't want or need more land, but that hasn't been enough to satisfy ranchers, who fear the proposal will resurface.

Now, Udall is offering a ban on expansion as an amendment to a Pentagon spending bill.

"The provision would prevent the Army from unilaterally expanding its footprint at Pinon Canyon - including through the use of eminent domain," Udall's office said in a news release.

The measure differs from previous congressional roadblocks to expansion in that it would require the Army to undergo an arduous process for any expansion effort to proceed.

The Army, meanwhile, has been mulling whether to pull a Defense Department provision authorizing future expansion of Pinon Canyon.

Then-Defense Secretary Donald Rumsfeld signed off on a waiver to Pentagon land acquisition rules. The waiver authorized the Army to seek more land in southeastern Colorado.

The Army in August said it would consider rescinding the waiver, but hasn't issued a decision.

"For the good of our ranchers, our soldiers and our state, it is time to put the Pinon Canyon controversy behind us. This common-sense, bipartisan amendment will give southern Colorado's ranchers and residents the certainty they need to focus on their livelihoods, while ensuring that Fort Carson's leaders are able to concentrate on providing their soldiers with the tough, realistic training the Pinon Canyon Maneuver Site offers," Udall said in a statement.