The legislation for the Biosecurity tax passed the House of Representatives this week, but the opposition to the concept from the Coalition, Greens and key cross-bench representatives should send the Government a clear message.
Grain Producers Australia chief executive Colin Bettles said the independent scrutiny of parliamentarians and lower house voting numbers had raised some "serious red flags."
The legislation has now been referred to the Senate Standing Committee on Rural and Regional Affairs and Transport.
"GPA also urges cross-bench Senators to follow the example set by their Lower House colleagues and meet with producers and their representative groups to understand the reasons why they strongly oppose this flawed proposal - including why it still remains unfair and inequitable, despite recent changes," he said.
"This is not about the rates charged to producers no matter how big or small - it's about core policy principles, standards and integrity."
The senate committee has been asked to report by May 10 and stakeholders have until April 10 to make a submission.
The levy is set to begin on July 1, it is not yet known if there will be public hearings.