The phrase "relentless campaign" means a continuous and persistent effort or series of actions towards a specific goal or purpose, without stopping or giving up. Full definition
Grayling accused his boss of running a «relentless campaign of fear». (theguardian.com)
by Tom Tanton, E&E Legal Director of Science and Technology Assessment As Appearing in The Sacramento Bee The Center of Biological Diversity's relentless campaign against domestic energy production in California has reached new lows for distortions and fear - mongering. (eelegal.org)
On the back of relentless campaigning by TIGA (the trade association representing the UK games industry), tax relief will now be offered for videogame developers in the UK. (thatvideogameblog.com)