“It is HARD ENOUGH for Frum people to get a job when others may very likely NOT WANT people that need to leave early Every Friday and Erev Yom Tov”
This is certainly discriminatory (on the basis of religion), and if it can be proven that an applicant was rejected for that reason, that employer will have a big problem on his (or her) hands.
I would appreciate if one of the Lawyers in Residence here in the CR would inform us laypeople whether the ads to which the OP refers are illegal. Is there anything wrong with wanting to hire, say, only females to preserve the religious acceptability of a workplace environment?