Oliver Coppard, a South Yorkshire mayoral candidate, visited the Advanced Manufacturing Research Centre (AMRC) in Rotherham, which is one of the university's sites, last Friday.
Bill Esterson, the Selton Central Labour MP, led the delegation as part of their efforts to demonstrate how manufacturing innovation leads to regional growth.
The Shadow Minister for Industrial Trade then tweeted about the visit, which subsequently earned the wrath of striking university staff who called them 'out of touch'.
Dr Jo Grady, a British trade union leader and the general secretary of the University and College Union, was one of the critics.
She tweeted: “Hi Bill, there's a picket line at Sheffield University.
“It's hard enough for our members to see management cross the picket lines let alone Labour MPs. You know better than this, surely? Let's hope this is a misunderstanding.”
‘I messed up and I’m sorry’
Mr Coppard, who was mentioned in Mr Esterson's tweet, then wrote an apology after he received a barrage of criticism following the visit.
He said: “Woke up, looked at Twitter and my mentions are full of people shouting at me and I can understand why.
“There was no visible protest or picket at the AMRC. But that doesn't change the fact that there was industrial action happening at the University of Sheffield and the AMRC is one of their sites.
“I didn't connect the dots and I should have. I messed up and I'm sorry.
“I'll be making a donation to the UCU strike fund by way of an apology and contacting my friend in Sheffield UCU to offer my apologies in person.”
He also stressed that he's ‘always supported UCU's fight to protect pay and conditions of staff’.
Mr Esterson, when pointed out about crossing the picket line, said: “Thanks Jo. There wasn't a picket line. Otherwise, I wouldn't have gone in."
UCU replied: “Hi Bill, on days we are on strike at any given situation, all university buildings are behind the picket line. Feel free to check with us in the future.”
The UCU has this week launched the largest wave of strike action in its history over pension cuts and ‘deteriorating’ pay and working conditions.