The workers are set to meet the Indian ambassador in Doha within the next two weeks to discuss their plight, Arvin Patil of the Indian Community Benevolent Forum charity told AFP.
The staff are thought to be employed by an Abu Dhabi-based firm.
"Around 300 to 400 people have not been paid," said Patil.
"We could give money if there were one or two people but 300 minimum is very, very difficult. We are interested in helping these people."
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Indians comprise the largest single group of expatriates in Qatar, numbering around 545,000 out of a total population of some 2.5 million.
The failure to pay them comes despite the introduction of a Wage Protection System (WPS) last November, meant to ensure that wages are paid electronically.
Bosses of firms which do not comply with the law face fines or imprisonment.
The WPS is a key reform introduced by the 2022 World Cup host in an attempt to improve labour conditions following widespread international criticism of Qatar's treatment of migrant workers.
In July, a senior Indian embassy staffer said there had been no calls to help feed labourers stranded without wages after losing their jobs, as has happened elsewhere in the region.
He told AFP this problem did not exist in Qatar.
Yesterday, staff at a hospital in eastern Saudi Arabia went on strike over unpaid wages.
The Qatar pay dispute comes at a time of belt-tightening in Doha because of falling gas and oil prices.
Qatar faces an estimated budget deficit of more than USD 12 billion in 2016, its first in 15 years, and officials have warned further deficits would follow in 2017 and 2018.
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