There's a fresh look at how transparent major companies are when it comes to their political activity.

More than two dozen companies on the Standard & Poor's 500 Index scored 90 percent or better, out of 100, in the new rankings.

The high ratings don't correlate with the companies' line of work. The top 28 included medical equipment manufacturer Becton, Dickinson and Co., railroads CSX and Norfolk Southern, AFLAC insurance, tech giants Microsoft and Intel, and drug maker Bristol-Myers Squibb.

Companies that scored zero included Berkshire Hathaway, Urban Outfitters and Netflix.

The annual reports have been produced for five years by the nonprofit Center for Political Accountability and the Zicklin Center for Business Ethics at the Wharton School, University of Pennsylvania. This is the first year the report covers the entire S&P 500.

"We've seen companies that are starting to restrict their spending," said Bruce Freed, the center's president. "We see the continued expansion of disclosure. Companies recognize that they need to address this." Scores are based on how much a company reveals to shareholders and the public, not on how it spends money in politics.

At Netflix, a company that scored zero with the CPA, spokeswoman Anne Marie Squeo said there was virtually no spending — just $14,900 so far this year, all disclosed through government agencies. Netflix gives nothing to superPACs, the U.S. Chamber of Commerce or politically active 501c4 groups, she said. Adding, "It's not our business model."

Corporate political action committees, funded by employees, already disclose their contributions by law, as do superPACs that accept corporate treasury funds.

But trade associations, business groups such as the U.S. Chamber of Commerce, and 501c4 "social welfare" groups have no disclosure requirement. Some firms earmark such funds for strictly non-political use.

Corporate political spending came under greater scrutiny after the Supreme Court's 2010 ruling known as Citizens United. The decision allows corporations and unions to spend directly in candidate campaigns, although they are still barred from giving directly to candidates.

This year corporations are being solicited by the presidential superPACs. In one example, Nextera Energy, an S&P 500 company in Florida, has given $1 million to Right To Rise USA, the superPAC supporting Jeb Bush.

At Altria, one of the top 28 companies, spokesman David Sutton said disclosure matters to shareholders. "It's important for them to be aware of what we do in this space" of politics, he said.

"This is a significant area of concern for corporate America now," said Robert Kelner, a Washington-based campaign finance lawyer with corporate clients. But he dismissed as "utterly false" one of CPA's central arguments: that shareholders have an economic interest in a company's political spending.

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