Very few airlines have zed or ID agreements for First Class (think this was discussed before) But we also need to distinguish between first and business class especially on long haul international flights. VS for example does not have a first class. Their highest class of service is business class which they cheekily market as "Upper Class" Many legacy carriers are slowly phasing out first class service and cabins alltogether. For us staff passengers flying zed on another carrier, it all depends on the agreement. Mainly among alliance partners there's the option to purchase business class, and fingers crossed and even more prayers than normal, you sit up front. Of course the tickets are more expensive. As sponge said UA and LH as founding members of Star Alliance perhaps, give their employees that option on each other's metal.

If you purchase your tickets via myidtravel you see clearly with whom you may purchase the business class zeds. Its divided into columns C ( for biz) and Y (economy class) then with low, medium or high price bracket