Sentence:  Since the metaphysical status of egg-casing is not one on which the church has yet pronounced, opposition appears based on "yuck" and nothing else. But yuck has become diktat, with Catholic MPs up to cabinet level being given a <WSD>three-line whip</WSD> by their bishops. 
Meaning of the word marked with <WSD> tags:  A directive to MPs from party leaders to vote in a particular way in parliament, despite what the MP might believe or what his or her constituents might like.