Anti-war activists say an injunction against their Brighton demonstrations would breach their right to protest.
Protesters blockaded the road outside EdoMBM last year
Arms firm EdoMBM Technology is trying to stop the Smash EDO campaigners from protesting outside its plant.
Stephanie Harrison, for seven of the defendants, said the injunction would have a "draconian and totally unjustified" impact on their rights.
On Friday, the High Court saw footage of a roadblock and a 24-hour rooftop occupation. The case continues.
'Mass murder' memo
The High Court claim has been brought by the managing director of EdoMBM, David Jones, on behalf of 156 Brighton employees, security guards, and three sub-contractors.
His representative, Tim Lawson-Cruttenden, claimed the factory had been targeted in a "concerted campaign" of unlawful harassment, with employees assaulted, intimidated and insulted.
Footage shown to Mr Justice Gross was of a roadblock last May which closed access to the site for five hours, and the rooftop protest in September.
The court heard a memo containing Mr Jones's address had linked him with "mass murder".
Protesters highlighted the firm's role in making arms systems
The court has been asked for an order under the Protection from Harassment act against 12 named individuals and two groups - Campaign to Smash EDO and the Bombs Out of Brighton Campaign.
The order would be in force until a full trial took place and would restrict all protests to four and a half hours on Thursday afternoons.
No more than 10 people would be allowed to attend, and artificial or amplified noise would be banned.
Protesters would also be stopped from having contact or seeking to communicate with the firm's employees.
There would also be an exclusion zone around the premises in Brighton.
But Ms Harrison said the protesters had rights of free association, expression and protest.
She said it concerned a matter of the most public controversy - the war in Iraq.
And she said it was impossible for the claimant to establish the required criminal standard of proof for its allegations that the two protest groups had run an anti-war campaign of which the individual defendants were a central part.
The hearing will continue on Monday.