Liverpool MP Paul Lynch said there is "no possible or proper justification" for the new toll motorists will be slugged with on the M5 East - a previously untolled road.
The distance-based toll will be $6.95 for cars and $20.86 for trucks. The toll coincides with opening of the new M8 motorway on Sunday, with the eight kilometre twin tunnels to run from from Kingsgrove to St Peters.
Mr Lynch said the decision to impose a new toll on the current M5 East from King Georges Road to General Holmes Drive is "disgraceful."
"This part of the road has been toll free since its opening in 2001," he said.
"For regular users of the M5 East that's going to be quite a substantial sum. Allowing it to happen when so many are suffering so many financial problems is just unreasonable.
"Presumably the government is using this new toll to cross-subsidise the new West Connex M8 - so users of the M5 East are having to pay for a road other than the one they're driving on."
NSW Labor urged the government to introduce a toll-free period on the M8 and scrap the new toll on the old M5 East.
"It will take people time to adjust to the new road, and people will want to explore the route and see if it works for them," said Labor's spokesman on roads John Graham.
"It's just greedy to throw a toll at motorists the second the road opens.
"The M5 East has been free since it opened in 2001 and there have been no upgrades. It's going to hurt motorists, families on tight budgets and it's going make it even harder for tradies and truckies to do business."
Camden MP Peter Sidgreaves said drivers should make use of the existing toll relief programs.
"The Premier has made it clear that there will be no grace period due to toll relief options like free registration or half-price registration from Service NSW," he said.
"There will be no cashback scheme on the M5 East but the cashback scheme in the south west will remain."
Mr Sidgreaves said the M5 East's capacity had doubled in recent years.
"I think it shaves at least 30 minutes off the trip, so that saves people an hour on a round trip," he said.
"If I could save that hour and spend it with my family I would expect, and be happy, to pay for it."
Transport Minister Andrew Constance said tolls "enable this infrastructure to be built generations ahead of time".
A Transport for NSW spokesman said the M8 tunnels would double the capacity on one of Sydney's most congested routes.
"This change was first announced in 2015 as part of the planning and community engagement for this vital $4.3 billion project. The M5 East was not built to handle the number of cars and trucks that rely on it daily," the spokesman said.
"The M5 East carries about 100,000 vehicles a day, and the toll reflects the significant travel time improvements many of these motorists will experience as a direct result of the M8.
"For example, motorists will save up to 30 minutes between Liverpool and South Sydney, with average travel times halved and peak hour speeds doubled.
"To prepare for the M8 a number of surface and in-tunnel works have been completed, including major surface works at Kingsgrove and resurfacing of the M5 East tunnels."
Bardia resident Lorry Parissakis will pay an extra $14 per day to use the same road he has used to get to his airport job for the past seven years.
He said the new toll would bring his daily commute to a total cost of $23.52 per day.
"On the Jobkeeper payment I can't afford to go to work with the new tolls along with paying the mortgage, bills and cost of fuel," he said.
"I would be basically paying to go to work which just isn't fair - it's highway robbery.
"There are some weeks where I might not be able to afford to go to work at all."
Macquarie Fields MP Anoulack Chanthivong said: "We aren't even getting any upgrades on the M5 East and it won't be eligible for the M5 cashback. This is just a big new toll on the same old road."