(Adds background on Cliffs, details on proxy put)
May 29 (Reuters) - An activist investor trying to win control of Cliffs Natural Resources Inc's board said on Thursday it may take the mining company to court over a "proxy put" that could trigger a liquidity crisis.
In a regulatory filing last week, Cliffs said it may be forced to repurchase its outstanding senior notes because of a change of control provision on the notes if all six of hedge fund Casablanca Capital's nominees were elected to its board.
Casablanca, which wants to replace Cliffs' chief executive and separate the company's U.S. assets from its international properties, said on Thursday that Cliffs could defuse the problem by approving its nominees "not as an endorsement, but merely for the narrow purpose of not triggering the proxy put."
"Instead of implementing this now-common corporate governance measure, the board has implied a willingness to put the company's very existence at risk, employing brinkmanship with the company's liquidity in an attempt to preserve its current seats," Casablanca said in a statement.
Casablanca said it would "protect shareholder interests by all available means, including litigation" if Cliffs did not approve its nominees.
In March 2013, a Delaware judge barred the board of Sandridge Energy Inc from resisting a proxy campaign by an activist fund, ruling the company could continue campaigning only if it approved the dissident nominees to avoid triggering a proxy put.
The carrying value of Cliffs' senior notes was $2.88 billion as of March 31, 2014, according to a recent filing, and it had $364 million in cash and equivalents.
Hit hard by a tough iron ore market and high costs at its Canadian operations, Cleveland-based Cliffs appointed a new CEO in February, and slashed capital spending, indefinitely suspending an expansion at its Bloom Lake mine in Quebec.
Cliffs did not immediately comment on the Casablanca statement.
(Reporting by Allison Martell; Editing by Bernadette Baum and Paul Simao)