"Anarchist pop group Chumbawamba performed their hit single "Tubthumping" live at the 1998 Brit Awards in support of the Liverpool dockers. They changed the words of the song to "New Labour sold out the dockers; just like they'll sell out the rest of us!" Later in the evening band member Danbert Nobacon jumped onto Deputy Prime Minister John Prescott's table proclaiming "This is for the Liverpool Dockworkers!" before emptying a bucket full of iced water all over him."
They sing a lot about workers rights and unions, maybe you are joking. "Boys on the Docks" is almost what you're after, but not saying directly to join a union.
Ken: It’s brand new. It’s about my grandfather, John Kelley. He organized most of the union workers down on the fish pier.