Labor opponents got what they bargained for when the nation’s top court held last year that forcing nonmembers to pay union fees violates the Constitution.But a union has struck back with its own challenge, claiming other parts of Illinois’ labor law are unconstitutional if so-called “fair-share” fees are.A federal judge this week allowed part of that challenge to go forward, ruling the union’s First Amendment claims against part of the Illinois Labor Relations Act are “far from …