In a statement released on Monday, Klaus said that neither the Czech Republic nor the whole EU needs such a regulation.
"There is no reason to further toughen legislation in this field. People are not endangered by chemicals," he added.
The bill, passed by parliament last month, implements an EU directive that requires manufacturers and importers to register chemicals with the new Helsinki-based European Chemicals Agency.
Klaus, a free-market proponent and long-time EU skeptic, says the new system is too costly, depriving Europe's chemical industry of competitiveness. The law is "an unprecedented step" that would place the Czech chemical industry "under the direct control of European bureaucrats," he said.
"It amounts to full subjugation of the whole chemical industry," Klaus added.
The new EU agency's tasks are to collect information and run a public database on chemicals as well as to evaluate, authorize and restrict use of substances, so they pose no hazard to humans and the environment.
The European Parliament approved the regulation in 2006. It entered into force in 2007. The 200-seat Czech parliament passed the law on July 18. At least 101 votes are needed to override Klaus' veto.