Twenty U.S. senators have asked Agriculture Secretary Tom Vilsack to take immediate action to include white potatoes in the Women Infants and Children food package. The letter didn’t state “or else,” but perhaps should have.

The May 2 bipartisan letter, signed by Sens. Susan Collins, R-Maine, Debbie Stabenow, D-Mich., Charles Schumer, D-N.Y., Mike Johanns, R-Neb., and 16 other senators, said the USDA’s decision to exclude potatoes from the WIC food package “remains unsatisfactory.” The senators argued that the nutritional value of potatoes would offer WIC participants needed potassium and dietary fiber and said current WIC rules were based on outdated dietary guidelines.

Collins, according to a report on Politico.com, is preparing an amendment for the Senate’s agricultural appropriation legislation later this month that would prevent the USDA from using any funds that would exclude any fresh vegetable from the WIC food package. Collins may have the necessary bipartisan support to pass the amendment, the report said.

A press spokesman for Collins was not available May 8.

Since 2009, WIC food packages for the estimated 9.1 million participants include monthly vouchers for fruit and vegetables that at the time ranged from $6 to $10 per participant. The combined value of those vouchers was estimated at close to $600 million per year by the Washington, D.C.-based United Fresh Produce Association.

In a controversial USDA regulation in 2008 that followed a recommendation of a 2005 Institute of Medicines report, white potatoes were excluded from the WIC fruit and vegetable vouchers because they were already widely consumed.

The five-year fight for white potato inclusion in WIC food packages has taken many forms.

Most recently, the fiscal year 2014 omnibus appropriations bill, passed by Congress signed by President Obama in January, directed the USDA to amend regulations to include all fresh and cut vegetables the WIC fresh produce vouchers, or else explain the exclusion to Congress.

The USDA didn’t change the program at that point, but the agency said it would speed its review of the WIC food packages.

Lawmakers said that wasn’t good enough. “While we note the Department’s decision to expedite its regular review of WIC in recognition of the expectation of Congress to include all varieties of fresh vegetables in the food package, we urge you to take immediate action to remedy the unwarranted exclusion of white potatoes in the WIC food package in light of more recent science,” the letter from the senators said.

Mark Szymanski, director of public relations at National Potato Council, said the potato industry is hopeful that both House and Senate lawmakers will support the inclusion of potatoes in the WIC food packages during the agricultural appropriations process later in the month.

“We think we have done a very good job of educating members and their staff on the importance of this issue,” he said. “It is an issue that has been going on forever so we hope by the end of the month we might have some resolution to it.”

While some nutrition advocates have bristled that members of Congress would try to direct the USDA on nutrition issues, Szymanski said the potato industry has tried to work with the USDA for many years to fix the problem through the regulatory process. “We feel that Congress has the appropriate oversight to perform its oversight of the WIC program,” he said. “Those who are concerned about opening a Pandora’s box to other products who want to get into the WIC food packages, we understand that is a concern - but potatoes are the only fresh fruit and vegetable not included in the program,” he said. “It is just closing loophole rather than opening the door to everything else.”