An LMIA, or Labour Market Impact Assessment, is an application submitted to Employment and Social Development Canada (Service Canada) to prove that the company needs a temporary foreign worker and that no Canadian citizen or permanent resident was found to meet this need.
LMIA is a lengthy and laborious process which, if successful, can allow the applicant to apply for a Work Permit. The final decision whether to issue a Work Permit or not rests with IRCC when it reviews the Work Permit application.
LMIA processing time varies from a few weeks to a few months. Once a positive LMIA is obtained, a Work Permit application must be filed within 6 months. Work permit applications are usually processed in a few weeks.
Immigration and Refugee Protection Regulations provide for a number of exemptions from LMIA. You might be exempt, if you fall under an international agreement or if hiring you is in the Canadian interests.
LMIA is also not required for some provincial nominee programs and for the Atlantic Immigration Pilot Program.