A plan to shift some farm subsidies into a revenue-protection measure may cost more than expected and won’t make necessary changes to agricultural programs, according to advocates for lower payments.

A bill backed by Democratic senators Richard Durbin of Illinois and Sherrod Brown of Ohio and Republicans Richard Lugar of Indiana and John Thune of South Dakota would consolidate several subsidy programs into a plan to aid farmers when revenue declines. The proposal would save $19.8 billion over 10 years, according to the Congressional Budget Office. The agriculture committees of both houses have pledged to come up with $23 billion in cuts by Nov. 1.