From Monday, lorry drivers face fines of up to £2,000 for each stowaway found hiding in their vehicles. Their lorries may also be seized.
Immigration Minister Barbara Roche handed out leaflets in Dover on Friday to publicise the new law.
But the Freight Transport Association says punishing drivers is not the answer.
"What is going to happen, I fear, is that instead of co-operating with the authorities, delivering these people to the immigration authorities or police, the fact that drivers are going to be fined £2,000 if they do that will mean they will just tip them at the roadside somewhere," said the association's spokesman Geoff Dosseter.
'Holding the baby'
He said: "This is like finding a burglar in your front room, calling the police and getting arrested for your trouble.
"We are now in the middle in the transport industry, holding the baby."
The association says more checks should be carried out by the French and Belgian authorities to stop the stowaways getting as far as the UK.
"I have been quite horrified when looking into this matter just to see sometimes how little precaution is taken. This is a very serious problem of people entering the country clandestinely," she told BBC Radio 4's Today programme.
"Very many of the applications we see for asylum are completely unfounded and people haven't made applications in the first safe country they come to.
"There is a trade in this, there is very big money in it and the government has to take very firm decisive action indeed."
The Freight Transport Association says it is is impossible for lorry drivers to be sure no-one has climbed aboard their vehicles.
But Ms Roche says simple measures, including securing vehicles, searching them, and using lightweight carbon dioxide detectors, could all be used.
She says the government has given the haulage industry considerable help in preparing for the change.
"There is a lot of carelessness that is going on. It has to be ended and that is why the civil penalty will be coming in on Monday," she said.
Another plank of the government's strategy to tackle the issue of asylum seekers was called into question on Friday.
'Sums wrong' claim
Channel 4 News said a draft report from the Audit Commission accused the government of getting its sums wrong in its plans to disperse asylum seekers around the country.
The Home Office was said to have underestimated the total cost by up to £30m.
A Home Office spokeswoman said she could not comment on the details of a leaked report.
A spokesman for the Audit Commission also declined to comment.
The dispersal plan, which comes into effect on Monday, aims to reduce the pressure on local authorities in Channel ports and London, by moving asylum seekers from the place where they enter the country to different locations around the UK.