Irish were strong presence in skilled mechanic trades, not just laboring jobs

Evidence

What stands out in the above list of Irish-dominated and -influenced unions is that, with the exception of the laborers, longshoremen, porters, and coachmen associations, all represented workers in the mechanic trades. This is not surprising to those familiar with the unionism of that era, which was largely a phenomenon of the mechanic trades, but it shows that, while the Irish made up the majority of laborers, they were also a strong presence in many trades with large populations of native-born whites and English and German immigrants. — Noel Ignatiev, How the Irish Became White, 415