Lost somewhat amid the exchange offer launch at Citigroup, was the announcement that the bank had adopted a "tax benefits preservation plan" that seeks to address an old tax law that might prevent the company from using its deferred tax assets if someone amassed more than 5 percent of the common stock.

CreditSights suggests that the plan may function as something of a poison pill. While the bank has said that it mainly aims to prevent someone from going over the 5 percent mark accidentally, the research firm remains skeptical. "Even if this measure was adopted to avoid triggering this negative tax consequence and preserve the value of the DTA, it seems to us to be a convenient way to avoid the possibility of other investors amassing a large stake in the company," it wrote in a report to clients. Citi did acknowledge that the plan could be a "disincentive" to anyone seeking a big stake. Citigroup's DTA stands at $43 billion.

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