Construction was a problem sector highlighted by the union in its pan-industry campaign.
It said a lack of female toilets on construction sites was a particular problem.
Unite said: “Women in particular are denied toilet dignity, especially when they are on their period.”
Unite is highlighting the problems today as it is World Toilet Day.
Unite assistant general secretary Gail Cartmail said: “The examples that Unite has revealed are simply staggering and it is clearly deeply humiliating for the workers who are being denied toilet dignity.
“Employers have got absolutely no excuse for ensuring toilet dignity and if they fail to do so they should be prosecuted by the HSE.
“Unite will not be passive on this issue, if workers are denied toilet dignity we will name and shame the guilty parties.”