PLAID leader Leanne Wood accused a Conservative MP who voted against plans for equal marriage of playing "politics by mailbag", during a recording for BBC Three programme, Free Speech, recorded in Swansea's Brangwyn Hall on Wednesday.
David Morris, MP for Morecambe and Lunesdale, said he voted against the equal marriage bill because "in my mailbag my constituents sent to me over 1,000 emails and letters and I had in the region of 15 that wanted me to vote for it. As a member of parliament, my job is to listen to my constituents, that's what I did".
But Ms Wood argued: "I can't believe politics is by mailbag.
"So if you had a mailbag full of people saying they wanted to bring back hanging, you would vote to bring back hanging?"
Free Speech was broadcast live, and the Swansea show focused on long-term unemployment, female harrassment and social media safety.
The show is broadcast every month and is available on BBC iPlayer after transmission.