We're having the same issue with our current employer.
The problem is the company won't sign off any PICUS time until you complete their "PICUS programme" which requires a simulator check which is planned at the company's whim. They have also issued an NTC to captains forbidding them from signing logbooks unless the FO is taking part in this PICUS program.
If you have 250 (or 500? can't remember exactly) hrs P1 by instructing etc before you get your first airline job then it's not a problem but if you need P1 U/S then you need the company to sign.
No idea why it would be illegal to keep a CPL when you've reached 1,500 hours??