Some staff working in London's financial district have been told to stay at home or wear casual clothing to protect themselves from May Day protesters.
Stockbrokers have hired extra security staff in case the demonstrations become violent.
The Corporation of London, which runs the Square Mile, has advised City firms to make sure somebody is on the door to stop protesters breaking in. They also urge companies to make sure their CCTV is working and issue door passes.
Some city workers are dressing less formally so protesters won't guess where they work.
Ms Annette Wrigley of Gerrard Stockbrokers says: "Some of our employees have decided to attend work in casual clothes today because of the May Day protests and some have worn casual clothes to the office before changing into their work clothes.
"There's a lot of different opinions about what will happen today but it's business as usual and we have taken sensible but not extreme precautions by enlisting extra security staff."
PA