Some US workers at Amazon and US food delivery firm Instacart are threatening strikes, and have accused the firms of not providing proper protections.
US senators have also written to Amazon boss Jeff Bezos to express concerns.
The companies have said they are taking extra precautions, amid booming demand for delivery services due to the virus.
"We are going to great lengths to keep the buildings extremely clean and help employees practice important precautions such as social distancing and other measures", an Amazon spokesman said in a statement.
"Those who don't want to work are welcome to use paid and unpaid time off options and we support them in doing so".
Amazon said it had adjusted its practices, including increasing cleaning of its facilities and introducing staggered shift and break times.
Mr Bezos earlier this month addressed the worries in an open letter to staff, thanking them for their work.
The company, which is looking to hire 100,000 more warehouse workers in the US to help address the surge in orders, has also said it would boost pay for warehouse staff around the world, including $2 per hour in the US and £2 per hour in the UK, where staff have been told to work overtime.
However, US lawmakers have questioned Amazon over reports of shortages of protective and cleaning supplies, as well as its sick leave policies.
The firm earlier faced strikes by workers in France and Italy and has been hit by legal complaints over the issues in Spain, according to a global alliance of unions coordinated by UNI Global Union.