Mr Straw said yesterday that drivers could virtually stop the stowaways overnight if they carried out simple checks on their trucks.
And he said he would go ahead with plans to fine truckers pounds 2,000 if illegal immigrants are found on their vehicles.
The Road Haulage Association, representing lorry firms, condemned the plans as "outrageous and unworkable".
"You don't need to be a genius to work out that if hauliers are about to be fined every time they voluntarily approach the authorities and disclose the presence of illegal immigrants, they will simply resort to releasing the illegal immigrants without informing the police," a spokesman said.
He said the association still hoped to change ministers' minds. The level of fines suggested - pounds 2,000 per illegal immigrant - could put some smaller truck firms out of business, he added.
But Mr Straw, writing in the News of the World, said almost 5,000 people were found hidden in freight vehicles in the first eight months of this year.Reuse content