No, oral or written contracts of service apply equally and are enforceable under the law.

Therefore, the absence of a written contract of employment does not stop any party to enforce it or to fulfil their obligations. 

The only difference is in the means of proving the existence of both

A Contract of Employment  is any agreement whether in writing or verbal, expressed or implied, whereby:

One person agrees to employ another as an employee; and

The other person agrees to serve the employer as an employee in return for remuneration/payment.

• To report to work as per the rules and regulation of the workplace.
• To do the work assigned to him/her by his employer. Only lawful assignment and engagements.
• To keep secrets of the workplace or job
• To respect the employer and fellow employees
• Not to endanger the workplace
• To follow the lawful rules and regulations of the workplace