Gary Olsen, known affectionately as "Gazza" or Gazzarooney" by his mates, is the Group Head for Corporate Finance in a boutique investment bank called "DA Bank Limited". There is a term in Gazza's employment contract, which he signed on 15 February 2020, providing as follows:

Prohibition on client contact. In the event that your employment with DA Bank Limited ceases for whatever reason and howsoever caused, you explicitly agree and undertake not to contact clients of DA Bank through whatever means. This includes contact by phone, email, mail or any other common means of communication. This prohibition will last for 3 years upon the cessation of your employment with the bank.

Gazza resigns from DA Bank on 1 March 2021. He is later recruited by his good mate Colin Taggart, who is the Chief Executive Officer of a merchant bank called "Tag Bank Limited". Upon joining, Colin immediately appoints Gazza to the same position that he held with DA Bank.

Gazza then starts calling some clients of DA Bank that he had dealt with when he worked there. DA Bank now wants to take legal action against Gazza.

Explain to DA Bank the grounds, if any, on which it can take legal action to stop Gazza from contacting the bank's clients.