Ten fines are issued to hauliers every day after migrants are found hiding in lorries, new figures show.
Home Office data shows 3,522 civil penalties were handed to drivers or their employers in 2016/17 after "clandestine entrants" were discovered in vehicles.
This was a 12% rise on the tally of 3,151 in the previous 12 months, according to statistics supplied following a Freedom of Information request.
A total of £7.8 million worth of fines were issued in the most recent year.
The findings suggest that large numbers of migrants are still boarding UK-bound lorries despite the closure of the Jungle camp in Calais in autumn last year.
The figures were obtained by law firm Nockolds, which claimed they raise doubt about the fairness of the penalty regime
A fine of up to £2,000 can be imposed on drivers or firms for each stowaway discovered where reasonable measures were not taken to secure and check vehicles.
A driver or haulier served with a civil penalty notice can lodge an objection or appeal against it.
Transport lawyer Dan Hart, of Nockolds, said: "The majority of drivers take measures to secure their vehicles but it is increasingly difficult to do so when faced with the determination of large gangs of migrants.
"If there are even the smallest shortcomings, civil penalties are imposed.
"In the current climate, it raises the question of whether the penalty regime is fair given the exceptional circumstances."
On Tuesday a van driver was killed in the port town after colliding with lorries reportedly forced to stop due to migrants blocking a road with tree trunks.
In a separate case, 18 people were found in the back of a lorry on the A22 in East Grinstead, West Sussex, on June 17.
The Road Haulage Association (RHA) has called for the French military to be deployed on the Calais approach roads to the port to protect UK-bound HGV drivers.
An RHA spokeswoman said: "Hauliers take every precaution possible to prevent migrants getting on the back of their trucks but it still happens.
"We regularly hear from hauliers who no longer want to take the Calais/Dover route because of the risk of fines and also the real possibility of facing intimidation or migrant attacks.
"This will harm the economy and inevitably lead to higher prices."
RHA chief executive Richard Burnett added: "The Clandestine Civil Penalty scheme to tackle lax and careless operators was introduced in 1999 at a time when the number of illegal migrants heading towards the UK was considerably less.
"The playing field has now changed and we believe that the scheme is outdated and must be reviewed."
Figures published last July showed that the number of migrants discovered in the UK after hiding in vehicles or on trains had more than doubled.
A report on so-called "lorry drops" showed authorities encountered 6,429 "clandestine entrants" in the six months from the beginning of April to the end of September 2015, compared to 2,411 in the same period of 2014.
A Home Office spokeswoman said: "It is in all our interests to combat attempts to enter the UK illegally, which can damage the haulage industry financially and place the safety of drivers at risk.
"That is why we continue to work closely with the French to bolster security at the ports, tackle the organised crime networks behind trafficking and people-smuggling, and ensure hauliers and other travellers can travel through the ports safely.
"Most hauliers take their responsibilities for vehicle security seriously - the fines imposed are designed to ensure that all drivers take reasonable measures."