FMCSA issues operating authority to foreign carriers, these authorities (aka MC number) does not allow foreign carrier to engage in any gainful activities other than deliver their Canadian or Mexican originated freight in US and pickup Canadian/Mexican bound freight delivering outside of US. 
However, these foreign carriers while in US, with the help of US freight brokers, continuously and increasingly engaging in Inter-stating activities prohibited by US Customs and Border Protection, US Citizenship and Immigration Service and other economic and trade regulations, NAFTA 1994, hence violating Americans economic rights, The Second Bill of Rights.
Inter-stating means a foreign carriers Loading their trucks in US with a load that delivers within US.
Cabotage Rule of US CBP [19 CFR § 123.14(c)] prohibits non-US trucker to load any freight that is delivering within USA. (https://www.dhs.gov/xlibrary/assets/policy/dhs-cross-border-trucking-guidelines.pdf
DHS & USCIS prohibits any gainful activity by non-US truckers. (https://www.dhs.gov/xlibrary/assets/policy/dhs-cross-border-trucking-guidelines.pdf

This petition is to unite and demand to establish a system of enforcement and ensure that US freight brokers and Canadian/Mexican motor carriers do not engage in US Inter-stating, a right of American trucker.
Foreign carriers bidding and offering freight brokers to move at much cheaper rates. Due to currency conversion and not taxed in US foreign carriers are a high profitability option for US freight brokers.
These foreign carriers affecting US Truck Load Ratio and underbidding to US freight brokers is becoming a major factor in low rates for US Truckers and Drivers pay.
(Ref: https://www.pstc.ca/cabotage-rules-canadian-driver/