London's Metropolitan Police have a list of 200 companies that they believe are likely to be targets where IT departments have been urged to step up security.
Some London-based organisations have planned for staff to work from home, while those coming into work have been advised to dress down.
Oil giant Shell is high on the protestors' list of potential targets. "We keep high security on IT facilities all of the time, not just for specific events," a spokesperson said. "We do not believe we are a specific target but we could be."
Banks are likely to be targeted. A spokesman for Barclays said, "This event highlights the security issue because it is so well publicised. We take security seriously all the time. It is a very important issue for us every day. The usual contingency plans are in place. Because we are a bank we always have to maintain high levels of security, be it physical or IT-based."
"Staff will be briefed and advised to be vigilant, and to use their common sense," he added.
A spokesman for Lloyds of London said, "We will be stepping up security [on Tuesday]. We have gone through a couple of these, but they have never touched us. We have security on the Lloyds building which stems back from the mid-1980s when there were a couple of bombs."
Clothing retailer Gap and supermarket Sainsbury's are taking advice from police. Sainsbury's was keeping tight-lipped as to what contingency plans it had made in the event of its stores or Web site being targeted by anti-capitalist protesters.
"We are just one of around 200 companies that have been advised by Scotland Yard. It would not be appropriate for us to comment further," said a representative.
A spokesperson for sports retailer Nike, also on the hit list, said, "We are taking special measures."
Fast-food chain McDonalds, another potential target, said, "We have been liaising with the police and authorities."