Police broke up “at least” 300 house parties across Scotland over the weekend, with 14 arrests being made.
More than 100 fines were issued between Friday and Sunday, with officers having to force entry to three households.
Police Scotland said its analysis suggested house parties were being held “in every community and age group”.
Chief Constable Iain Livingstone said most people were following the rules – but “decisive action” would be taken where necessary.
New rules barring indoor meetings of more than six people from two households have been introduced in Scotland in response to increasing numbers of Covid cases.
Pubs have also been ordered to close by 22:00, and additional police officers were sent out to support councils over the first weekend of the new restrictions.
Mr Livingstone said officers would “use good sense and exercise discretion”, and that “the great majority of people are taking personal responsibility to do the right thing”.
But he added: “There can be no excuse for arranging, attending, or hosting a house party.
“It is against the law. Where officers encounter blatant, wilful, or persistent breaches, we will take decisive action to enforce the law.”
First Minister Nicola Sturgeon said the figures had to be seen in the context of a country with a population of 5.4 million people.
She said “the vast majority” were abiding by the rules.
“Anybody who is not, and particularly anybody who is who are fragrantly breaking very clear rules against house parties, should really take a look at themselves,” she added.
“We know that house parties are one of the risk factors that can cause this virus to spread.”
While officers were called to a number of parties at student halls in Edinburgh, Ms Sturgeon stressed that the issue with indoor gatherings was not just about young people.
Mr Livingstone said on Friday that analysis suggested that only one in 10 house parties police responded to had been linked to students.