New measures to tackle animal rights extremists and protect researchers have come into force.
Research on animals is vital, the government says
Police can now order protesters who target employees of animal research companies at their homes to leave and not return within three months.
There are also tougher powers to protect individuals against harassment.
A new offence of "harassment intended to deter lawful activities" has been created as part of the Serious Organised Crime and Police Act.
The UK pharmaceutical and biotechnology industry provides "more than 22,000 jobs and [is] worth more than £3.6 billion in the UK," said Trade and Industry Secretary Alan Johnson.
"Companies have the right to conduct legitimate business free from fear of being attacked," he added.
Health Secretary Patricia Hewitt said the activities of animal rights extremists endangered vital research into cancer, HIV/Aids and Alzheimer's Disease.
While protesters have the right to campaign lawfully against the use of animals in scientific research, Home Office minister Paul Goggins said: "They do not have the right to engage in acts of intimidation or violence against individuals and firms working in this area."
Call for police
Huntingdon Life Sciences, long a target of extremists, welcomed the tougher laws but called for sufficient police resources to implement them.
Director Brian Cass said: "I continue to be encouraged by the robust and determined position that the government is taking to control animal rights extremists."
The measures were also welcomed by the chief executive of BioIndustry, Aisling Burnand.
"This legislation will serve to eliminate the grey area in which animal extremists have previously operated, and will protect companies and individuals engaged in legitimate, groundbreaking bioscience research in this country and, crucially, all those connected with the research.
"The challenge now is to ensure that the police and the judiciary have the resources they need to implement these new laws."
A spokesman for anti-vivisection campaign Speak said the law was "ambiguous and open-ended".
"It is encouraging people to go down the road of illegal activity, because when you restrict a person's democratic right to protest then they will have not other option," Robert Cogswell said, while emphasising that the Speak campaign operated legally.
The British Union of the Abolition of Vivisection said it was concerned the measures "will constitute a serious threat to freedom of expression for anyone who opposes animal experiments making it an offence, for example, to cause economic damage".
It asked: "Could this mean that exerting economic pressure will be illegal for anti-vivisectionists, however peacefully and reasonably they behave?"