Senate opponents of stripping military commanders of the authority to prosecute serious crimes such as rape and sexual assault said Monday that the proposal could make it worse for victims.

In a letter to Senate colleagues, 11 members of the Senate Armed Services Committee wrote that sexual assault in the military is an abomination and must be dealt with forcefully, but they rejected the solution offered by Senator Kirsten Gillibrand, a New York Democrat.

Gillibrand has the public support of nearly half the Senate for removing commanders from deciding whether serious crimes go to trial and giving that authority to seasoned trial lawyers who have prosecutorial experience and hold the rank of colonel or higher.

"We believe strongly that this would create a system that would actually be worse for victims and significantly undermine the military system of justice and discipline," the senators wrote. "It could lead to constitutional hurdles for military prosecutions; undermine the ability of prosecutors to execute plea bargains that can spare victims a difficult trial process."

The senators also said the plan would undercut the ability of commanders to threaten courts-martial and carry out non-judicial punishments.

Gillibrand insists that victims don't trust the chain of command to mete out justice, or that they fear or have experienced witness retaliation. She points to the Pentagon estimate of 26,000 military members who may have been sexually assaulted last year, based on an anonymous survey. Thousands of victims were unwilling to come forward despite new oversight and assistance programs aimed at curbing the crimes, the Pentagon said.

The letter comes ahead of a showdown over the issue as Gillibrand is expected to offer her plan as an amendment to the annual defense policy bill. The proposal has bitterly divided the Senate and the 26-member Armed Services Committee.

Senators Carl Levin, a Michigan Democrat, and Jim Inhofe, an Oklahoma Republican, the top members of the panel, signed the letter as did female senators Claire McCaskill (Democrat, Missouri), Kelly Ayotte (Republican, New Hampshire), and Deb Fischer (Republican, Nebraska).

Backing Gillibrand are Senators Ted Cruz (Republican, Texas), and Rand Paul (Republican, Kentucky), as well as 16 of the Senate's 20 female members.

The Associated Press obtained a copy of the letter.