The congressmen called proposed guidance from the Financial Action Taskforce "concerning."
ETC's first industry report also shows second-quarter Ethereum transaction volume increased more than 2,000%.
Accumulation by miners is analogous to increased promoter holding of corporate stock and is considered a positive.
Daily miner revenue has risen above $3 million this week.
"Miners may be holding in anticipation of a price rally," one analyst said.
Miner outflows have slowed since January. The last time this happened, bitcoin went parabolic.
The deal will also see the two firms work together to develop miners built to Argo’s specifications.
Bitcoin fell sharply early on Monday, having failed to establish a foothold above $40,000 over the weekend.
Bitcoin mining equipment maker Ebang announced Thursday it is preparing to officially launch a cryptocurrency exchange in the first quarter of 2021.
The announcement comes after a holiday weekend in which the price of bitcoin hit a succession of new all-time highs.
The Thanos upgrade is aimed to allow more miner participation and thus increase security.
Chinese miners are struggling to sell their crypto in ways that would quickly get them much-needed cash in the face of a government crackdown on local exchanges.
Bitcoin's transaction activity has cooled amid the recent lull in price action – and that's hurting miners' earnings.
Nasdaq-listed bitcoin miner manufacturer Ebang said the pandemic had disrupted its supply chain and led to a significant drop in revenue.
Bitcoin miners, following the law of supply and demand, curtailed their supply to exchanges to the lowest level in 12 months during the second quarter.