WASHINGTON (Reuters) - More than 100 chief executives of some of the nation’s most well-known companies on Thursday called on the U.S. Senate to take action to tackle gun violence, including expanding background checks and strengthening so-called red flag laws, according to media reports.

In a letter to lawmakers, 145 company heads urged meaningful action following a string of mass shootings across the United States that have most recently left communities reeling in Texas, Ohio, Nevada and South Carolina.

“Doing nothing about America’s gun violence crisis is simply unacceptable and it is time to stand with the American public on gun safety,” the letter to the Republican-led U.S. Senate said, according to the New York Times, which first reported the correspondence.

Those signing the missive include the heads of Gap Inc, Levi Strauss & Co, and Dick’s Sporting Goods Inc. They also included Royal Caribbean Cruises Ltd, Uber Technologies Inc, Twitter Inc, and Amalgamated Bank, among others.

“We are writing to you because we have a responsibility and obligation to stand up for the safety of our employees, customers and all Americans in the communities we serve across the country,” they said, according to the Times. The Washington Post also reported the letter.

Lawmakers have struggled to address gun violence after the 2012 killing of 26 people, including 20 children, at Sandy Hook Elementary School in Connecticut stoked debate over gun control in America.

More mass shootings followed, including at a church in South Carolina, a music festival in Las Vegas and a high school in Florida. This summer, shootings in Dayton, Ohio, and El Paso, Texas - including in a Walmart - sparked fresh debate.

Walmart Inc and other stores have since called on patrons not to openly carry firearms in their stores, prompting protests from opponents who object to curbing gun rights.

The U.S. House of Representatives, led by Democrats, quickly took up measures addressing gun violence as lawmakers returned to Washington this week. These include three bills that seek to remove guns from people deemed a risk, ban high-capacity ammunition magazines and prohibit people convicted of violent hate crime misdemeanors from possessing firearms.

The Senate, led by President Donald Trump’s fellow Republicans, has so far stayed on the sidelines, with Senate Majority Leader Mitch McConnell looking to the White House for guidance.

On Wednesday, a bipartisan group of U.S. senators said they wanted to revive a failed 2013 bill to close loopholes on the law requiring gun sale background checks, but it remained unclear whether Trump would support it.

Polls have shows that nearly half of all Americans expect another mass shooting to happen soon in the United States.