This problem was proved to be NP-complete in https://link.springer.com/article/10.1007/BF00340774,
- J. Nešetřil, V. Rödl, Complexity of diagrams, Order 3 (1987) 321–330, https://doi.org/10.1007/BF00340774,
but a mistake was discovered, and later corrected, for a simple proof and brief history, see https://link.springer.com/article/10.1007%2FBF01108825.
- G. Brightwell, On the complexity of diagram testing, Order 10 (1993) 297–303, https://doi.org/10.1007/BF01108825.
I've asked the same question myself earlier this year from some people working in the field, the above links were given to me by Piotr Micek. Some papers to read are also given in https://arxiv.org/pdf/1908.08250.pdf
- Janos Pach, Istvan Tomon, Coloring Hasse diagrams and disjointness graphs of curves, https://arxiv.org/abs/1908.08250v1
on page 2, before Theorem 1. Also see https://link.springer.com/article/10.1007/BF00400288.
- B. Bollobás, G. Brightwell & J. Nešetřil, Random graphs and covering graphs of posets, Order 3 (1986) 245–255, https://doi.org/10.1007/BF00400288.