Tata Sons, owners of Tata Steel, replaced "lame duck" Cyrus Mistry with his predecessor Ratan Tata last week.
Tata Steel employs almost 7,000 workers around Wales, including more than 4,000 at its plant in Port Talbot.
Community Union said Tata must now engage in discussions on the long-term future for steelmaking in Europe.
In a joint statement Community's general secretary Roy Rickhuss and Frits van Wieringen, chairman of the Tata Steel European Works Council, said: "The news that Cyrus Mistry has been removed as chairman came as a surprise to us all.
"However we wish Ratan Tata well in taking over the reins at this challenging time for Tata Steel Europe.
"At this time we are asking Tata to alleviate the uncertainty for the workforce, customers and suppliers, by clarifying the situation regarding the strategic direction of the European operations.
"Furthermore, it is imperative Tata now engage with us to discuss their long-term vision and plans for steelmaking Europe."
Mr Mistry has lashed out at the way his sudden departure was handled.
In a no-holds-barred email to the board seen by the BBC, Mr Mistry said he had become a "lame duck" chairman and alleges constant interference, including being asked to sign off on deals he knew little about.
He also warned the company risks huge writedowns across the business.
Tata said it currently had no response to the allegations.
Last week, Tata Steel's UK head Bimlendra Jha praised the "significant effort" to turn things around - after Port Talbot was said to be losing Â£1m a day earlier this year.
Tata looked to sell its UK business, but paused the process in July.
Losses at Port Talbot have been reduced by a turnaround plan and better market conditions such as rising steel prices and a drop in the pound's value.
Steel unions have said a decision by the Indian-owned giant Tata to replace its chairman came as a surprise to its workforces across Europe.