The freedom of a hen to flap its wings and move around became an issue of congressional concern Thursday as a Senate committee discussed legislation to set national standards for the treatment of egg-laying hens.

WASHINGTON — In this Congress, even eggs can cause a political stir.

An effort by Sen. Dianne Feinstein, D-Calif., to establish a national standard for the cages in which hens lay eggs has run afoul of farm-state lawmakers.

The conflict was on display at a Senate Agriculture Committee hearing Thursday.

Feinstein’s bill drew support from many egg producers who turned up at the Capitol, but it also generated concerns from Republican senators.

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“Why would the federal government want to drive up costs on one of the staples of their diet?” Sen. Pat Roberts, R-Kan., said, suggesting the legislation could increase egg prices. Sen. Charles Grassley, R-Iowa, added, “Some states have passed bad laws that are hurting their egg producers and consumers, and now they want to fix it by putting nonscience-based restrictions on all egg farmers.”

Feinstein’s bill grew out of California voter approval in 2008 of a measure requiring chicken farmers to give egg-laying birds enough room to stand and spread their wings. At least five other states have enacted similar rules, creating a patchwork of standards that has complicated operations for egg producers.

The legislation was patterned after a compromise reached last year between the Humane Society of the United States and United Egg Producers, whose members produce 90 percent of all eggs sold in the United States.

David Lathem, chairman of United Egg Producers and a Georgia poultry farmer, said the deal would allow his industry to plan for the future where “the American public is interested as never before in where food comes from.”

Greg Herbruck, a poultry farmer from Michigan, told the packed hearing room that his farm sells eggs in 30 states and that with individual state standards “we could have to have a chicken house for every state.”

But Amon Baer, a Minnesota farmer, said, “The problems of one state or even a handful of states does not justify a federal mandate on all 50 states.”

Feinstein’s Egg Products Inspection Act Amendments’ would establish a national standard for the “humane” treatment of egg-laying hens and the labeling of eggs, including increasing the size of hen cages.

Her legislation is opposed by a number of farm groups, including the beef, pork and sheep industries, which signed a letter contending the legislation could set a “dangerous precedent for allowing the federal government to dictate everything that happens on farms.”

Republicans have advocated national standards on other matters, such as when California sought to regulate greenhouse-gas emissions from vehicles, contending it was preferable to a patchwork of state laws.

Prospects for the bill are uncertain. Feinstein was thwarted in efforts to include the measure in the Senate farm bill.

An effort is under way in the Republican-controlled House to block states from imposing their own standards for agriculture products on producers from other states. The effort comes in response to the California law, which will take effect in 2015, that requires that all eggs sold in the state to be produced by hens held in cages that meet the California standards.

According to the United Egg Producers, most of the nation’s 280 million hens are provided 67 square inches of space, with roughly 50 million receiving 48 square inches. After the phase-in, the birds would have a minimum of 124 to 144 square inches of space.

Material from The Associated Press is included in this report.