Slough will face the toughest level of measures when England's national lockdown finishes next week.
The government has announced the local authority area will be in the "very high" alert tier three from 2 December.
Slough Borough Council said the number of the cases was falling but not "quickly enough".
The measures mean pubs and restaurants will remain closed in the town, and no mixing between households is allowed indoors or in private gardens.
However people can meet in groups of six in outdoor public spaces, and non-essential shops, gyms, and personal care services will all reopen.
Lead member for health councillor Natasa Pantelic said: "Unfortunately cases in Slough, though coming down, are not dropping significantly or quickly enough putting Slough people at risk.
"While this risk remains so high, I call on all residents to follow the lockdown rules until 2 December and then stick to the regulations of our new tier to protect themselves, their families and communities from what can be a devastating illness."
Although Slough has seen a dip in the number of cases, it still has the highest infection rate in Berkshire with 313.6 cases per 100,000 as of Thursday, according to the Local Democracy Reporting Service (LDRS).
Reading, Wokingham, Bracknell Forest, Windsor and Maidenhead and West Berkshire will go into tier two on 2 December.
It comes as it was announced most of England will be place in the two toughest levels of measures when lockdown ends.