Is late payment of the holiday allowance permitted because of the coronavirus outbreak?

Most employees in the Netherlands expect to receive their holiday allowance in the month of May or June. However, this year, due to the financial difficulties caused by the coronavirus outbreak, some employees fear that their employer may be, at best, reluctant to pay out the holiday allowance on time and, at worst, unable to pay the holiday allowance at all. One of the trade unions, CNV, has reported that 8% of its members have stated that their employer will not be paying the holiday allowance that is due to them. Is this permitted by law?