Thousands of Edinburgh residents are likely to miss out on next month's congestion charging referendum.
Edinburgh plans to follow London in introducing the measures
About 30,000 had failed to declare their interest by Friday, when voter registration was due to close.
The rules mean anyone who ticked a box to avoid junk mail when filling in the electoral roll cannot take part in the vote unless they re-register.
Edinburgh City Council said it had extended the deadline to include any forms received in the post on Monday.
Almost 90% of the city's 330,000 registered voters should be eligible when the ballot on a series of transport proposals, including congestion charging, takes place in February.
The council wants two cordons, one inside the capital's ring road, the other round the city centre.
A £2 charge would apply from 0700-1830 at the inner cordon and 0700-1000 at the outer boundary on weekdays.
Cars and lorries are already forbidden from travelling east along Princes Street and the council wanted to extend the ban to westbound traffic.
Sarah Boyack is backing the proposals
London introduced a £5-a-day charge for entering a central zone in February 2003.
Mike Pringle, the Liberal Democrat MSP for Edinburgh South, said: "We are in favour of a scheme which will work; the scheme in Edinburgh is not going to work."
Mary Mulligan, Labour MSP for Linlithgow, added: "My constituents have limited options when the trains are full and the buses are full. They're using their cars to get into Edinburgh."
However, Labour Edinburgh Central MSP Sarah Boyack, a former transport and environment minister, said she would vote for the plans in next month's referendum.
She said: "If we don't do something we're going to end up with the city grinding to a halt."
Fellow backer, the Scottish Greens' co-convener Robin Harper, said: "Nobody has given a better answer or even an attempt at a better answer to the problems that are going to face Edinburgh over the next few years as traffic increases."