Complex sentence: From December 11,1975, to April 1976, service on the SIRT was shut down because the line's 61 motormen and conductors went on strike, which once they voted to receive 14% wage increases.
Split into simpler sentences: From December 11,1975 to April 1976, service on the SIRT was shutdown because the line's 61 motormen and conductors went on strike. The strike ended once they voted to receive 14% wage increases.