The action follows similar events earlier this month, when employees at a Sony factory in southwest France held two bosses hostage, a move that eventually led to secured improved terms for workers facing redundancy.
The country is undergoing a severe economic crisis and two massive public demonstrations have been held in recent weeks.
On Wednesday, the labour ministry announced that the number of unemployed people in France had jumped by 79,900 to 2.38 million in February - a smaller rise than the 90,000 who lost their jobs in January.
Rousselet, who is being held in his office, with a wardrobe blocking the door, said workers had "more to complain about than me and I knew there was this risk when I came here".
Workers at the plant have not threatened Rousselet with any violence and he has so far been allowed a toilet break.
Jean-Francois Caparros, a union representative, said: "This action is our only currency. But there is no aggression.
"Until we have a commitment from 3M that they will increase pay-packets and are ready to discuss our conditions for negotiations, then Mr Rousselet will have to remain here.
"If he wants to involve the police, then he will have to send for them, but it is out of [the] question that he leaves without discussing our conditions."
The action comes as vandals smashed windows and damaged a car at the home of Sir Fred Goodwin, former Royal Bank of Scotland chief, who sparked public anger in Britain when he refused to give up his large pension after the government rescued his bank.
Police in Edinburgh, the capital of Scotland, said Goodwin's large detached house was attacked in the early hours of Wednesday morning.