WASHINGTON — The House began to consider legislation Wednesday that would allow some schools to opt out of healthier meal standards — a proposal that has drawn a veto threat from the White House.

The GOP spending bill on the House floor would allow schools to waive the school lunch and breakfast standards championed by first lady Michelle Obama for the next school year if they lost money on meal programs over a six-month period. The chamber is expected to have a final vote on the bill next week.

In a statement threatening a veto, the White House said Tuesday that the bill would be “a major step backwards for the health of American children by undermining the effort to provide kids with more nutritious food.”

The school meal rules set by Congress and the Obama administration over the past several years require more fruits, vegetables and whole grains in the lunch line. Also, there are limits on sodium, sugar and fat.

Some school nutrition directors have lobbied for a break, saying the rules have proved to be costly and restrictive. The schools pushing for changes say limits on sodium and requirements for more whole grains are particularly challenging, while some school officials say kids are throwing away fruits and vegetables they are required to take.

Republicans have said the standards are overreach. Rep. Robert Aderholt of Alabama, the Republican author of the agriculture spending bill that includes the provision, said the rules were put in place too quickly and schools need more time to comply. On the House floor, he emphasized that the waivers are meant to be temporary.

“This is a real problem in many school districts across the country,” Aderholt said. “It only allows schools more time if they need it.”

California Rep. Sam Farr, the top Democrat on the agriculture spending panel, called the provision a “cop-out.” He held a rally on Capitol Hill Wednesday with parents, chefs and lawmakers to protest the opt-out language and is expected to offer an amendment to strip out the provision.

Mrs. Obama has lobbied Congress to keep the standards, holding a White House event late last month with school nutrition directors who said the guidelines are working in their schools. On Thursday, she is scheduled to harvest crops from the White House kitchen garden with school nutrition directors and children from schools that have successfully put the standards in place.

The Senate did not include the opt-out language in its version of the spending bill.