Resolute said it has been reducing the risk of transmission by limiting the travel of non-essential workers from outside the surrounding region to the mine site.
Resolute is now considering how to respond, while telling the union the strike notice is "irresponsible, opportunistic and represents a breach of … commitments".
The West Africa miner's full-year guidance had been 430,000 ounces at all-in sustaining costs of US$980 per ounce, with 260,000oz of that contributed by Syama.
Resolute's net debt at June 30 was $220 million.
Shares in Resolute fell 4.5% Wednesday and were down another 12% to 93c in morning trade today, capitalising the company at $1 billion.