I don't think IELTS are required for applying for work permit!
I believe for Skill Level C/D, it is required to have "Basic Proficiency" when it comes to English knowledge. 
CLB/NCLC 4 is considered “Basic Proficiency” and means that an individual being tested who “meets” CLB/NCLC 4:
can communicate basic needs and personal experience;
can follow, with considerable effort, simple formal and informal conversations;
can read a simple set of instructions, plain language; and
can write short messages, postcards, notes or directions.
 
- Listening 4.5  Reading 3.5    Writing 4.0  Speaking 4.0 -