The Tour de France, the world's most prestigious road cycling race, is starting in Utrecht, The Netherlands, on Saturday, 4 July, and will conclude as always in Paris after 21 days and 3,360 kilometres.
The ACP union said police will block the convoy of road vehicles that runs ahead of the main body of racers on the second day of the race as it crosses the 800 metre-long Erasmus Bridge across the Maas River in Rotterdam.
They will maintain the blockade until cyclists can be seen at a standstill because of the protest.
Frontline patrol officers in the Netherlands have been targeting high-profile sporting events in their dispute with the country's justice ministry. Last month, a first division soccer match was cancelled after police said they could not guarantee its security. The Tour de France will be the first international event they are targeting.
"After more than three months of actions, in which we have taken into account the interests of the public in mind as much as possible, our collective bargaining conflict with (justice minister Ard) van der Steur has not been resolved," the ACP union said.
"It is high time for the government to make us a reasonable offer."
Police said they had chosen the bridge since no spectators would line that section of the route, minimising any risk to the public.
The organisers of the Tour de France said they had no comment.