U.S. Senator John McCain (R-AZ) speaks after being awarded the 2017 Liberty Medal by former U.S. Vice President Joe Biden (unseen) at the Independence Hall in Philadelphia, Pennsylvania, U.S. October 16, 2017. REUTERS/Charles Mostoller

(Reuters) - U.S. legislation that would impose new disclosure requirements on political ads that run on Facebook and other websites received support on Wednesday from Senator John McCain, giving a bipartisan boost to a bill already popular among Democrats.

McCain, a longtime supporter of regulating campaign finances, and two Democratic senators, Amy Klobuchar and Mark Warner, plan to introduce the legislation on Thursday, according to a statement from their offices on Wednesday.

Republicans control the U.S. Senate and House of Representatives, so bills generally need Republican support to advance.

Online political ads are much more loosely regulated in the United States than political ads on television, radio and satellite services.

The lack of regulation was highlighted last month when Facebook Inc, Alphabet Inc’s Google and Twitter Inc said that they had found election-related ad buys on their services made by people in Russia in the run-up to last year’s U.S. presidential election. Non-Americans are generally not allowed to spend money to influence U.S. elections.

The legislation from the three senators would put online ads under the same rules as television, radio and satellite, so that who paid for them and other information would need to be disclosed.

Last month, after U.S. regulators and criminal investigators began looking at the Russia-linked ads, Facebook Chief Executive Mark Zuckerberg said his company would take several voluntary steps to make political ads more transparent, such as allowing anyone to seem them no matter whom they target.

Facebook and Twitter said on Wednesday that they are open to working with lawmakers on the matter. Google did not immediately respond to a request for comment.

McCain’s office declined to comment.