Rail, Maritime and Transport union boss Steve Hedley has been suspended after saying he would "throw a party" if Boris Johnson dies of coronavirus.
It comes after the Prime Minister was admitted into intensive care as he battled with Covid-19.
He was moved back to the ward at St Thomas' Hospital on Thursday as his condition improved.
Mr Hedley, who is the assistant chief of the RMT, is believed to have made comments on social media about having a party, in reference to Boris Johnson's condition.
He also reportedly wrote that he hoped the whole Cabinet contracted the deadly virus in a series of comments on his public Facebook profile.
The union boss then proceeded to hit back at users who criticised him for his comments.
Mr Hedley is a longstanding RMT official and is effectively the union's number two.
A spokesman for the union said: "Following a meeting of the union's National Executive a decision has been made to suspend senior assistant general secretary Steve Hedley with immediate effect while a formal investigation takes place into his conduct."
In a joint statement RMT president Michelle Rodgers and general decretary Mick Cash said: "Steve Hedley's comments do not represent the views of this trade union and are wholly unacceptable."
