WASHINGTON, Jan 11 (Reuters) - Steel industry and union groups on Monday urged President-elect Joe Biden to keep in place the 25% national security tariffs on steel imports imposed in 2018 by his predecessor, arguing they are essential to ensure the viability of domestic steel production.

In a letter to Biden, the American Iron and Steel Institute, the Steel Manufacturers Association, the United Steelworkers union, the Committee on Pipe and Tube Imports and the American Institute of Steel Construction said that the industry was starting to recover from COVID-19 shutdowns but remains "very vulnerable" to new surges in imports.

The groups said that excess global steelmaking capacity, already 700 million tonnes above demand, was expected to grow further as China, Vietnam, Turkey and other countries add production. Steel exports from South Korea, Russia, Ukraine and Indonesia also continue to increase, the groups said.

"Continuation of the tariffs and quotas is essential to ensuring the viability of the domestic steel industry in the face of this massive and growing excess steel capacity," they said in the letter https://www.steel.org/wp-content/uploads/2021/01/Steel-Coalition-Letter-to-President-Elect-Biden-011121.pdf. "Removing or weakening of these measures before major steel producing countries eliminate their overcapacity -- and the subsidies and other trade-distorting policies that have fueled the steel crisis -- will only invite a new surge in imports with devastating effects to domestic steel producers and their workers."

Democrat Biden told the United Steelworkers last May that he would keep Republican President Donald Trump's steel and aluminum tariffs in place until a global solution to excess production capacity can be negotiated. Since then, he has said he will not make any changes to tariffs until after he consults with U.S. allies.

Trump's Commerce Department imposed the Section 232 metals tariffs -- 25% on steel and 10% on aluminum -- in March 2018. According to data from the American Iron and Steel Institute, the tariffs have reduced the market share of imported steel to about 18% in 2020 from nearly 30% in 2017. (Reporting by David Lawder; editing by Jonathan Oatis)