I’m not knowledgeable about maritime union history but here’s a couple items I’ve come across. Not attempting to be “fair and balanced” with these link, just a different perspective.
The 1949 Canadian Seamen’s Union Strike – Frank & Ella Hatheway Labour Exhibit Centre
The story of the 1949 Canadian Seamen’s Union (CSU) strike is an appalling story in the history of the Canadian labour movement and indeed Canadian history in general. It is a story about anti-union shipping companies, who demonstrated a blatant disregard for the law, about a corrupt rival International union that was known for its unlawful violent activities,
The CSU was born out of the struggle against the barbaric working and living conditions that existed onboard the Canadian Merchant Fleet and it was the union of choice for the Canadian seamen.
When the CSU again opened negotiations with the shipping companies, in 1949, the companies had a new scheme to get rid of the union. While demanding major concessions from the CSU the shipping companies were, unbeknown to the union, negotiating behind their back with the corrupt Seafarers International Union (SIU). The SIU was based in New York
THE HISTORY OF UNION RIVALRIES: 45 YEARS LATER, AMO KEEPS CRANKING (paywall)
Today’s rivalry for ship officers’ jobs began in 1949, when the Brotherhood of Marine Engineers was founded by Paul Hall, Seafarers International Union president, to compete with the Marine Engineers Beneficial Association.