(I'm not sure I've got an answer, but I've got some research that may help someone else find a better answer).
The practice appears to be commonplace in European commercial and industrial applications.
In commercial and industrial applications (delivery times, production plans, etc.), especially in Europe, it is often required to refer to a week of a year. Week 01 of a year is per definition the first week that has the Thursday in this year, which is equivalent to the week that contains the fourth day of January. In other words, the first week of a new year is the week that has the majority of its days in the new year. Week 01 might also contain days from the previous year and the week before week 01 of a year is the last week (52 or 53) of the previous year even if it contains days from the new year. A week starts with Monday (day 1) and ends with Sunday (day 7). For example, the first week of the year 1997 lasts from 1996-12-30 to 1997-01-05 and can be written in standard notation as 1997-W01 or 1997W01 Kuhn
. . . for applications like industrial planning where many things like shift rotations are organized per week and knowing the week number and the day of the week is more handy than knowing the day of the month. Ibid
Mr. Geerkens points out
"More likely to come from manufacturing organizations that have a payday every Friday. For most businesses the most important planning expenditure has always been payroll."
This week numbering scheme was introduced earlier by the ISO with the standard ISO 2015:1976 (Numbering of Weeks) and was repealed on 1 June 1988 with the imminent introduction of ISO 8601. The calendar defined in the ISO standards 2015 and 8601 is commonly referred to as the “ISO calendar”. Gent
Implies that while this may have been common practice, it was introduced by ISO. I think it more likely that Mr. Geerkens is correct and this merely codified an existing practice.