Birch Telecom Inc. said Tuesday it had laid off 330 employees, or a third of its work force, as the telephone company continues to struggle under new rules restricting its access to local phone lines.

The company, which has dropped from 1,100 employees earlier this year to 525, said a majority of the layoffs were in field sales offices in Kansas, Texas, Oklahoma and Missouri, including 81 at the company’s headquarters in Kansas City, Mo. The company laid off 87 employees last month.

Birch is one of several smaller telecom companies that grew up from the Telecommunications Act of 1996.

The act sought to increase competition in the industry by forcing the regional Bell companies to lease space on their local phone lines to competitors for government-set prices.

The Federal Communications Commission earlier this year eliminated that requirement, allowing the Bells to negotiate new, and higher, terms.

Birch said the FCC’s decision would drive up costs and affect 90 percent of the company’s 500,000 access lines.