* Investigation of consumer complaint to last 6-9 months
* Merger would create Latin America's biggest airline
* LAN stock down over 2 pct, TAM falls more than 3 pct (Updates with stock price, LAN comment)
SANTIAGO, March 18 (Reuters) - Chile's LAN Airlines LAN.SN (LFL.N) said on Friday a regulatory investigation could delay its proposed merger with Brazil's TAM TAMM4.SA TAM.N, as the duration of the probe is uncertain.
LAN said it hoped Chile's antitrust tribunal (TDLC) would approve the deal by the end of the second quarter; but even so, the airline said it would be impossible to merge the companies, forming Latin America's largest carrier, before the fourth quarter,
The Chilean regulator said on Thursday it would investigate a consumer complaint against the proposed merger, saying the probe could take six to nine months.
"It is likely that a satisfactory outcome of this process will delay the merger, which, once approved, could not take place before the fourth quarter," LAN said in a statement.
The tribunal's move comes after Brazil's civil aviation authority gave the proposed merger the green light with no restrictions earlier this month, though approval of other Brazilian regulators is still pending. [ID:nN03126214]
LAN, one of Latin America's most profitable airlines, had said on Jan. 19 that the merger could take up to nine months pending approval from authorities in both countries. [ID:nN19206493]
LAN shares fell 2.32 percent to 11,815 pesos on Friday afternoon, after hitting their lowest level since last July, before the two companies announced the merger.
TAM stock was down 3.57 percent to 31.91 reais, also hitting its lowest level since the merger was announced in August. (Reporting by Santiago Newsroom; Editing by Steve Orlofsky and Gerald E. McCormick)