Complex sentence: Since longshoremen were prepared to walk out if an employer refused to accept a worker dispatched from the hall, the ILA soon controlled hiring on the docks, causing the employers to complain that the union wanted to "sovietize" the waterfront.
Split into simpler sentences: Since longshoremen were prepared to walk out if an employer didn't hire a worker dispatched from the hall, the ILA soon controlled hiring on the docks. The employers complained that the union wanted to "sovietize" the waterfront.