That's happening in all modern countries right now and the correct way to combat this downturn instead of letting companies go bankrupt or do layoffs. Do your research and you will see that this is not controversial at all.
If the alternative is getting laid off, I'm happy to accept the cut as I did last week.
That is standard in Germany. For a period of upto 12 months during emergencies, employees contracts can be reduced to x% (for x % hours), the govt will cover the remaining money (upto 60% of net salary). Its called shotrt-term work or kurzarbeit.
That also exists in France (and is currently used extensively) but it's very different from reducing salaries.
Employee must agree. Most do with their initial contract or because of unions, though.