WASHINGTON — Senator Amy Klobuchar, the top Democrat on the Senate Judiciary Committee's antitrust panel, said on Friday that she had re-introduced two bills aimed at strengthening enforcement of U.S. antitrust law.

One of the bills would adjust fees paid to the Federal Trade Commission and Justice Department's Antitrust Division for merger reviews, raising fees on bigger deals while smaller deals would pay less.

Klobuchar also introduced a bill to toughen standards for reviewing mergers. Under that bill, companies planning some large mergers would be required to show that their deal would not materially harm competition. Under current law, it is the government which must show that the deal would "substantially" harm competition.

The first bill was co-sponsored by Democratic Senators Tammy Baldwin, Richard Blumenthal, Cory Booker, Dick Durbin, Mazie Hirono, Patrick Leahy and Ed Markey, as well as independent Angus King, Klobuchar's office said in a statement.

The second bill was also co-sponsored by Blumenthal, Booker and Markey.

The bill that would adjust fees has the support of Makan Delrahim, head of the antitrust division, and FTC Chairman Joe Simons, whose agencies reviews deals - many valued at over $1 billion - to ensure they are legal under antitrust law. Both men were appointed by President Donald Trump.

The Justice Department is awaiting an appeals court decision on its bid to stop AT&T from buying Time Warner and is reviewing a planned merger by T-Mobile and Sprint, which would reduce the number of national wireless carriers from four to three.

The FTC is looking at a merger of dialysis companies Fresenius Medical Care and NxStage Medical Inc, as well as Altria Group's investment in vaping company Juul Labs Inc.