"We have been informed that Sangma has received an extortion note in the form of a text message. We are looking into it," said Director General of Police Prem Singh.
Sangma told a news agency, "I have received a number of text messages from the GNLA asking me to contribute Rs 5 lakh to the outfit or else they will kidnap and kill me."
"They (GNLA) made similar extortion demands earlier also but I did not pay heed," the legislator said.
Intelligence officials said the outlawed GNLA had slapped extortion demands ranging from Rs 5 lakh to Rs 1 crore on petrol vend owners, coal dealers and businessmen in the coal-rich districts of Garo Hills.
On Monday, police arrested coal dealer Uttam Marak for attempting to handover Rs 3.85 lakh to a GNLA rebel at a school playground in South Garo Hills district, bordering Bangladesh.