The European Commission has accused some of the world's biggest chemical firms of illegally fixing prices.
ICI said that the EC probe related to a former acrylics business
Among those accused are UK companies Imperial Chemicals Industries and Lucite, and Germany's BASF and Degussa.
The Commission says chemicals companies have been exchanging confidential market data and operated a cartel in the methacrylate-monomers market.
Methacrylate-monomers are used to make transparent plastics and coatings used in cars and consumer goods.
The Reuters news agency said that more than 12 firms could be involved in the investigation.
EC spokeswoman Antonia Mochan said the chemicals firms were suspected of fixing prices, passing around customers, sharing commercially sensitive information and discussing plans to pass on extra costs to clients.
"We have decided to open formal proceedings against a large number of European producers," she said.
Ms Mochan did not name the companies or say how many had been charged.
The firms will now have the chance to defend themselves against the allegations, but could be fined up to 10% of their annual sales if they are found guilty.
On Monday, ICI said the allegations against it involved a period between 1995 and 1999.
ICI, which sold its acrylics business in 1999, said it would "continue to assist the European Commission with its investigation".
A spokeswoman for Degussa said the firm had received a statement of objections from the EC over an alleged cartel case. She added that the company had adequate provisions to cover possible risks.
BASF and Lucite also confirmed they were being looked into.