"To strengthen the law" means to make laws more effective, powerful, or stricter in order to ensure they are followed and to enhance their impact on society. Full definition
The government proposes to strengthen laws against depictions of extreme sexual violence on the internet. (newlawjournal.co.uk)
The government will also say it is getting legal advice on how to strengthen the law so that if couples split up, their children can have a strong relationship with both parents. (theguardian.com)
An inquiry will be launched into the deaths and options weighed up, including strengthening laws and introducing mandatory health and safety duties on company directors. (politics.co.uk)