As outlined in the March 22, 2017 Federal Budget, the government proposed that professionals (accountant, dentist, lawyer, medical doctor, veterinarian or chiropractor other professionals are excluded) would be required to include work in progress (work that has occurred to the end of the taxation year but has not been billed at the end of the taxation year) in income for income tax purposes. It was announced that this would be phased in over a two-year period.  Previously a professional could elect to exclude work in progress from income, which allowed a professional to include work in progress in income in the year that the work was billed.  The changes will be applicable to taxation years that begin after March 22, 2017.  For professionals that have a taxation year end of December 31st, the new rules would be applicable to the 2018 and future taxation years.
On September 8, 2017, draft legislation was issued that propose to have the phase in period occur over a five-year period, instead of a two-year period as originally proposed.  The changes will operate as follows for taxation years beginning after March 22, 2017:

This transitional rule is only available to a professional who elected to exclude work in progress in the last taxation year that began before March 22, 2017.

One of the matters that professionals will now need to deal with as a result of these proposed changes is how to determine the cost of work in progress and how to determine the fair market value of work in progress.  As of the date of writing, I could not find any guidance from the Minister of Finance or the Canada Revenue Agency on this matter.  Stay tuned for possible further details.