The number of companies earning top marks for how they treat their LGBT employees has increased over the last year, according to a new report released Monday by the nation's largest LGBT rights group.

The Human Rights Campaign's (HRC) 12th annual Corporate Equality Index (CEI) ranks 304 companies with a perfect score, up from 252 last year.

HRC ranked each company on several gay, lesbian, bisexual and transgender workplace policies and assigned a rating from 0- to 100- percent.

Companies with a perfect score receive the group's coveted Best Places to work for LGBT Equality designation.

“This will go down in history as the year that corporate support for equality left the boardroom and reached each and every corner of this country,” HRC President Chad Griffin said in a statement. “Not only do fair-minded companies guarantee fair treatment to millions of LGBT employees in all 50 states, but now those same companies are fighting for full legal equality in state legislatures, in the halls of Congress and before the U.S. Supreme Court.”

Thirteen of the top 20 Fortune-ranked companies scored a 100 percent rating, including Chevron (Fortune rank 3), General Motors (5), General Electric (6), Ford Motor Co. (9), Hewlett-Packard (10), AT&T (11), Bank of America (13), McKesson Corp. (14), Verizon Communications (15), JPMorgan Chase (16), Apple (17), IBM (19), and Citigroup (20).

Verizon and Wal-Mart greatly increased their presence. Two years ago, Verizon scored only 20 percent. Wal-Mart, which recently announced it would offer benefits to the spouses of gay workers, increased from 60 to 80 percent.

Berkshire Hathaway's score decreased from 15 percent two years ago to zero. Exxon Mobil Corp. once again received a -25 percent score.

The report found that more than two-thirds of Fortune 500 companies and 90 percent of all large corporations it surveyed have extended benefits to the spouses of gay workers.

A record number of companies have added transgender protections to their workplace policies. They include 61 percent of the Fortune 500 and 86 percent of the 737 companies surveyed.

(HRC 2014 Corporate Equality Index.)