General Restrictions:
* Limitation: "The new law imposed a limitation on free speech."
* Constraint: "There were constraints on the amount of money they could spend."
* Restriction: (This is the most direct noun, but can sometimes feel too formal or literal)
* Regulation: "The government imposed regulations on the industry."
Specific Types of Restriction:
* Control: (Indicates a stronger, more active form of restriction) "The company exercised control over its employees' work schedules."
* Censorship: (For restrictions on information or expression) "There was censorship of the news during the war."
* Ban: (For complete prohibition) "There was a ban on smoking in public places."
* Curb: (For limiting something that is considered excessive) "The city council implemented curbs on traffic congestion."
More abstract concepts:
* Boundary: (For a line that defines what is and isn't allowed) "The company established boundaries for employee behavior."
* Parameter: (For a defined limit or range) "The project has specific parameters that must be followed."
* Condition: (For a requirement that must be met) "They were granted access under certain conditions.
Ultimately, the best noun to use will depend on the specific context of your sentence. Consider what you want to emphasize about the restriction: its severity, its purpose, or its specific nature.