Chembio Diagnostics Inc. plans to sell more stock to raise up to $21.2 million to fund acquisitions, factory improvements and other activities, executives said Tuesday.

The Medford-based manufacturer of rapid tests for HIV, Ebola, Zika and other diseases has established an “at-the-market” program with the Cantor Fitzgerald & Co. brokerage in Manhattan.

The program involves the sale of Chembio shares at the market price with the timing of the sale decided by the company, the officials said.

No shares have yet been sold under the program; up to 3.3 million shares will be sold over time, according to a securities filing.

The program “is an important tool that will be used in a disciplined manner to support growth opportunities, specifically including acquisitions and investments in manufacturing operations, and other corporate purchases,” acting CEO Sharon Klugewicz said in a statement.

A voicemail message seeking further comment wasn’t immediately returned Tuesday night.

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The planned sale comes less than a year after Chembio raised $12.8 million by selling 2.3 million shares priced at $6. The proceeds from that sale are being used to pay for test development, clinical trials, marketing and other activities, executives said in August 2016.

After completion of the stock sale announced Tuesday, the company would have 15.6 million outstanding shares, according to the securities filing.

The announcement came after the stock market closed on Tuesday. Chembio shares were unchanged at $6.35 in after-hours trading on the Nasdaq Stock Market. They are down 25 percent in the past 12 months.

The company reported a loss of $13.4 million last year on sales of $17.9 million.

About 130 people work at the Chembio facilities in Medford and Holbrook.