Updated from 11:58 a.m. EST

SAN FRANCISCO -- New York's attorney general announced Thursday that is it has started an antitrust investigation of Intel ( INTC).

Intel was served with a wide-ranging subpoena seeking documents and information as part of an investigation into whether the chipmaker violated state and federal antitrust laws by coercing customers to exclude rival Advanced Micro Devices ( AMD) from the microprocessor market.

"After careful review, we have determined that questions raised about Intel's potential anticompetitive conduct warrant a full and factual investigation," said NY Attorney General Andrew Cuomo in a statement.

Shares of Intel finished Thursday off 21 cents to $22.54.

AMD shares shot up as much as 8.2% at one point, the stock's biggest one-day move since Dec. 14, 2006. The stock later gave up some of the gain, finishing up 44 cents to $5.97.

AMD sued Intel in a Delaware federal court in 2005, alleging that the microprocessor giant has consistently abused its monopoly position in the market to prevent PC vendors from using AMD chips. A trial date has been set for April 27, 2009.

New York is the latest of several government regulators around the world to look into allegations that Intel has unfairly used its dominance of the PC microprocessor market to sideline AMD.

On Monday, Intel filed its response to charges relating to similar allegations brought by the European Commission.

The New York probe further complicates the legal situation for Intel.

The New York attorney general said its investigation will look into whether Intel penalized PC makers who brought microprocessors from AMD, and whether Intel improperly paid PC makers to exclusively use its own chips.

An Intel representative was not immediately available for comment.

David Balto, who was one of the lead attorneys at the Federal Trade Commission during an investigation of Intel in the late 1990s, said that the state attorney general has the same powers as the federal government in prosecuting antitrust cases.

"Anything the FTC can do, the state can do," said Balto.

But he noted that federal regulators could eventually join in.

"Frequently, federal enforcers do act after state enforcers have begun an investigation," said Balto.

New York's attorney general has a track record of prosecuting antitrust cases, including its participation in the suit against Microsoft ( MSFT). But the decision to take the lead in probing Intel has raised some eyebrows , given the state's relationship with AMD.

In June 2006, AMD announced a deal with NY state giving the chipmaker the option to build a $3.2 billion chip manufacturing facility in upstate NY -- one of the largest private investments in New York history.

AMD has until 2009 to decide whether to build the facility in order to garner subsidies from New York state, although the company's recent talk of outsourcing more of its chip manufacturing to third-party contractors may mean the fab never gets built.

A spokesperson for the New York attorney general would not comment on any possible relationship between that state's probe of Intel and AMD's plans in NY, or on any other matter beyond what was stated on the announcement.

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