Four months after the Senate defeated a Genetically Engineered labeling bill (S.2609) introduced by Agriculture Committee Chairman Pat Roberts (R-KS), the upper chamber Thursday night passed, 63-30, a compromise measure (S. 764) that Roberts co-wrote with Senator Debbie Stabenow (D-MI), the Ag Committee’s Ranking Member.

Unlike Roberts’s original bill, he and Stabenow’s version would mandate the labeling of food with genetically engineered ingredients (i.e., ingredients that have been altered such that they could not be reproduced through conventional breeding). The bill requires that labels appear either as an on-pack, USDA-created symbol or a QR or bar code that smartphones could read.

In a disappointment to some labeling advocates, the bill would preempt state laws, including Vermont’s Act 120, which took effect July 1st.  The bill has fewer exemptions than the Vermont law, which does not require labeling for tens of thousands of processed food products. However, it does exempt foods in which meat, poultry, or egg products are the main ingredient.

Critics also complain that the definition of “bio-engineering” under the bill is too narrow and would allow certain products to be excluded , e.g. canola oil and high fructose corn syrup due to the manner in which they are processed.

The bill does call for the USDA, rather than the legislature, through the rulemaking process, to permit stakeholders to determine the foods, ingredients, and processes that should be included or excluded from the labeling requirements

After the Senate voted to invoke cloture, Roberts conceded his bill is “not the best possible bill” but insisted that “it’s the best bill possible under the difficult circumstances we find ourselves in today.” Vermont Senators Patrick Leahy and Bernie Sanders took to the floor to argue otherwise (though they were overshadowed by a protestor in the gallery who threw $2,000 on to the Senate floor amid shouts of “Monsanto Money”).

Although the bill garnered strong bipartisan support and was co-authored by Ag Committee leaders, its future is uncertain. While Secretary of Agriculture Tom Vilsack has called for a national uniform labeling standard, President Obama has been noticeably tight-lipped. In the end, he may not have to take a position: Given long-standing opposition among House Republicans to mandatory labeling, a bill may not land on the President’s desk.

But with the clock ticking – Congress adjourns at the end of this week for its summer recess – and the prospect of Vermont’s law becoming the de facto labeling standard, skeptics of mandatory GE labeling may hold their nose and back the bill. It might their best choice, as the bill, according to Roberts, is the “last train that is leaving town.”

Sam Rothbloom is co-author of this article.