WASHINGTON (Reuters) - Republican and Democratic U.S. senators introduced legislation on Wednesday to discourage Taiwan’s few remaining allies from switching their allegiance to China, after El Salvador became the third country this year to move towards Beijing.

The legislation, introduced by Republican Senators Cory Gardner and Marco Rubio and Democrats Ed Markey and Bob Menendez, would authorise the State Department to downgrade U.S. relations with any government that shifts away from Taiwan, and to suspend or alter U.S. assistance.

It also requires a U.S. strategy to engage with governments to support Taiwan’s diplomatic recognition or strengthen unofficial ties with Taiwan.

Gardner, chairman of the Senate Foreign Relations Committee’s Asia subcommittee, discussed his plans for the legislation in an interview with Reuters last week.

The State Department had said the United States was “deeply disappointed” by El Salvador’s decision and was reviewing its relationship with San Salvador, without elaborating further.

Washington does not recognise Taipei diplomatically but considers it a staunch ally in the Pacific Rim. Several members of Congress, who see Beijing as a threat to U.S. security and international influence, have expressed frustration with what they see as President Donald Trump’s failure to adopt a strategy for Taiwan.